Method and apparatus for efficiently transmitting control information to support uplink multiple antenna transmission

ABSTRACT

The present invention relates to a method for transmitting control information regarding uplink multiple antenna transmission may comprise the steps of: transmitting DCI for scheduling the uplink transmission of a plurality of data blocks through a PDCCH; receiving the plurality of data blocks scheduled by the DCI; transmitting information which indicates positive acknowledgement or negative acknowledgement to each of the plurality of received data blocks through the PHICH; and receiving retransmission for the negative acknowledged data blocks. When the number of the negative-acknowledged data blocks is not equal to the number data blocks indicated in the PDCCH, a pre-coding matrix, which is for the number of transmission layers equivalent to that of layers corresponding to the negative-acknowledged data blocks, may be used for retransmission.

This application is a continuation of U.S. patent application Ser. No.13/637,978, filed on Sep. 27, 2012, now U.S. Pat. No. 8,848,600, whichis the National Stage filing under 35 U.S.C. 371 of InternationalApplication No. PCT/KR2011/002153, filed on Mar. 29, 2011, which claimsthe benefit of earlier filing date and right of priority to KoreanPatent Application No. 10-2011-0028302, filed on Mar. 29, 2011, and alsoclaims the benefit of U.S. Provisional Application Nos. 61/318,780,filed on Mar. 29, 2010, 61/325,346, filed on Apr. 18, 2010, 61/353,663,filed on Jun. 11, 2010, and 61/359,280, filed on Jun. 28, 2010, thecontents of which are all hereby incorporated by reference herein intheir entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly to a method and apparatus for transmitting efficientcontrol information to support uplink multiple input multiple output(MIMO) transmission.

BACKGROUND ART

A Multiple Input Multiple Output (MIMO) scheme refers to a scheme forimproving data transmission/reception efficiency using multiple transmitantennas and multiple receive antennas, unlike a scheme using onetransmit antenna and one receive antenna. That is, a transmitter or areceiver of a wireless communication system uses multiple antennas so asto increase capacity or improve performance. The MIMO scheme may becalled a multiple antenna technique.

In the multiple antenna transmission technique, there are a singlecodeword (SCW) scheme for simultaneously transmitting N data streamsusing one channel encoding block and a multiple codeword (MCW) schemefor transmitting N data streams using M (here, M is always equal to orless than N) channel encoding blocks. At this time, each channelencoding block generates an independent codeword and each codeword isdesigned to facilitate independent error detection.

In a system for transmitting multiple codewords, a receiver needs toinform a transmitter of success/failure of detection (decoding) of eachcodeword. Thus, the receiver may transmit a hybrid automatic repeatrequest (HARQ) ACK/NACK signal for each codeword to the transmitter.

In case of uplink data transmission through a single antenna, singlecodeword (SCW) transmission can be supported. In addition, a synchronousHARQ scheme can be applied to single antenna uplink transmission, and anadaptive or non-adaptive HARQ scheme can be utilized according towhether a modulation and coding scheme (MCS) is changed duringretransmission.

DISCLOSURE Technical Problem

Accordingly, the present invention is directed to a method and apparatusfor transmitting efficient control information to support uplink MIMOtransmission, that substantially obviate one or more problems due tolimitations and disadvantages of the related art.

Since the legacy 3GPP LTE system defines only HARQ operations for uplinksingle codeword transmission of a UE including a single antenna, thereis a need to define not only HARQ operations for uplink MCW transmissionand retransmission of a UE including multiple antennas, but also amethod for constructing control information capable of supporting theHARQ operations.

An object of the present invention is to provide a method and apparatusfor providing control information that is capable of efficiently andcorrectly supporting uplink MIMO transmission. In more detail, inassociation with HARQ operations for uplink MCW transmission, thepresent invention provides a method for constructing control informationon a Physical Hybrid-automatic repeat request (ARQ) Indicator CHannel(PHICH), a method for selecting a precoder, a method for selecting PHICHresources, a method for selecting a demodulation reference signal(DMRS), a method for performing UE HARQ operations through a PHICH and aphysical downlink control channel (PDCCH), and a method for constructingdownlink control information (DCI) on a PDCCH.

It will be appreciated by persons skilled in the art that the objectsthat can be achieved through the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention can achieve will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting control information of uplink (UL) MIMO(Multiple Input Multiple Output) transmission by a base station (BS),the method including transmitting downlink control information (DCI)scheduling UL transmission of a plurality of transport blocks to a userequipment (UE) through a physical downlink control channel (PDCCH);receiving the plurality of transport blocks scheduled by the DCI fromthe user equipment (UE); transmitting information indicatingacknowledgement (ACK) or negative acknowledgement (NACK) of each of thereceived transport blocks to the user equipment (UE) through a physicalhybrid-automatic repeat request indicator channel (PHICH); and receivingretransmission of a transport block indicating NACK from the userequipment (UE), wherein, if the number of NACK transport blocks isdifferent from the number of a plurality of transport blocks indicatedby the PDCCH, a precoding matrix for the same number of transmissionlayers as the number of layers corresponding to the NACK transport blockis used in the retransmission.

In another aspect of the present invention, a method for performinguplink (UL) MIMO (Multiple Input Multiple Output) transmission by a userequipment (UE) includes receiving downlink control information (DCI)scheduling UL transmission of a plurality of transport blocks from abase station (BS) through a physical downlink control channel (PDCCH);transmitting the plurality of transport blocks (TBs) scheduled by theDCI to the base station (BS); receiving information indicatingacknowledgement (ACK) or negative acknowledgement (NACK) of each of thetransmitted transport blocks from the base station (BS) through aphysical hybrid-automatic repeat request indicator channel (PHICH); andtransmitting retransmission of a transport block indicating NACK to thebase station (BS), wherein, if the number of NACK transport blocks isdifferent from the number of a plurality of transport blocks indicatedby the PDCCH, a precoding matrix for the same number of transmissionlayers as the number of layers corresponding to the NACK transport blockis used in the retransmission.

In another aspect of the present invention, a base station (BS) fortransmitting control information of uplink (UL) MIMO (Multiple InputMultiple Output) transmission includes a reception module for receivingan uplink signal from a user equipment (UE); a transmission module fortransmitting a downlink signal to the user equipment (UE); and aprocessor for controlling the base station (BS) including the receptionmodule and the transmission module, wherein the processor enables thetransmission module to transmit downlink control information (DCI)scheduling UL transmission of a plurality of transport blocks to a userequipment (UE) through a physical downlink control channel (PDCCH),enables the reception module to receive the plurality of transportblocks scheduled by the DCI from the user equipment (UE), enables thetransmission module to transmit information indicating acknowledgement(ACK) or negative acknowledgement (NACK) of each of the receivedtransport blocks to the user equipment (UE) through a physicalhybrid-automatic repeat request indicator channel (PHICH), and enablesthe reception module to receive retransmission of a transport blockindicating NACK from the user equipment (UE), wherein, if the number ofNACK transport blocks is different from the number of a plurality oftransport blocks indicated by the PDCCH, a precoding matrix for the samenumber of transmission layers as the number of layers corresponding tothe NACK transport block is used in the retransmission.

In another aspect of the present invention, a user equipment (UE) forperforming uplink (UL) MIMO (Multiple Input Multiple Output)transmission includes a reception module for receiving a downlink signalfrom a base station (BS); a transmission module for transmitting anuplink signal to the base station (BS); and a processor for controllingthe user equipment (UE) including the reception module and thetransmission module, wherein the processor enables the reception moduleto receive downlink control information (DCI) scheduling UL transmissionof a plurality of transport blocks from the base station (BS) through aphysical downlink control channel (PDCCH), enables the transmissionmodule to transmit the plurality of transport blocks (TBs) scheduled bythe DCI to the base station (BS), enables the reception module toreceive information indicating acknowledgement (ACK) or negativeacknowledgement (NACK) of each of the transmitted transport blocks fromthe base station (BS) through a physical hybrid-automatic repeat requestindicator channel (PHICH), and enables the transmission module totransmit retransmission of a transport block indicating NACK to the basestation (BS), wherein, if the number of NACK transport blocks isdifferent from the number of a plurality of transport blocks indicatedby the PDCCH, a precoding matrix for the same number of transmissionlayers as the number of layers corresponding to the NACK transport blockis used in the retransmission.

The following contents can be commonly applied to the above-mentionedembodiments.

The retransmission may be carried out if a PDCCH is not detected in adownlink subframe in which the UE detects the PHICH.

The precoding matrix may be a specific precoding matrix for the samenumber of transmission layers as the number of layers corresponding tothe NACK transport block, from among a plurality of precoding matricesindicated by the most recent PDCCH.

A subframe performing the retransmission at the UE may be a fourthsubframe starting from a subframe in which the UE receives the PHICH.

One PHICH resource may be allocated to one transport block (TB).

One transport block (TB) may be mapped to a single codeword, and thesingle codeword is mapped to one or two layers.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

Exemplary embodiments of the present invention have the followingeffects. The embodiments of the present invention can construct controlinformation capable of supporting the HARQ operation for uplink MIMOtransmission and the MCW transmission operation, etc., such that theuplink MIMO transmission can be correctly and efficiently performed. Inmore detail, in association with HARQ operations for uplink MCWtransmission, the present invention provides a method for constructingcontrol information on a Physical Hybrid-automatic repeat request (ARQ)Indicator CHannel (PHICH), a method for selecting a precoder, a methodfor selecting PHICH rsources, a method for selecting a demodulationreference signal (DMRS), a method for performing UE HARQ operationsthrough a PHICH and a physical downlink control channel (PDCCH), and amethod for constructing downlink control information (DCI) on a PDCCH.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved through the present invention are not limited towhat has been particularly described hereinabove and other advantages ofthe present invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing the structure of a downlink radio frame.

FIG. 2 is a diagram showing an example of a resource grid in onedownlink slot.

FIG. 3 is a diagram showing the structure of a downlink subframe.

FIG. 4 is a diagram showing the structure of an uplink frame.

FIG. 5 is a diagram showing the configuration of a wirelesscommunication system having multiple antennas.

FIG. 6 is a conceptual diagram illustrating codebook-based precoding.

FIG. 7 is a conceptual diagram illustrating an SC-FDMA transmissionscheme and an OFDMA transmission scheme.

FIG. 8 is a block diagram illustrating MIMO transmission based on uplinkmultiple codewords.

FIG. 9 is a conceptual diagram illustrating uplink MIMO transmissionusing a precoder subset.

FIG. 10 is a flowchart illustrating uplink MIMO transmission andreception methods according to embodiments of the present invention.

FIG. 11 is a block diagram illustrating a base station (BS) and a userequipment (BS) applicable to embodiments of the present invention.

BEST MODE

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toanother. Some components or characteristics of any embodiment may alsobe included in other embodiments, or may be replaced with those of theother embodiments as necessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between a base station and a terminal.In this case, the base station is used as a terminal node of a networkvia which the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “Base Station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with a Relay Node (RN) ora Relay Station (RS). The term “terminal” may also be replaced with aUser Equipment (UE), a Mobile Station (MS), a Mobile Subscriber Station(MSS) or a Subscriber Station (SS) as necessary. While the followingdescription exemplarily uses a UE or a relay node (RN) as an uplinktransmission entity and exemplarily uses a BS (eNB) or RN as an uplinkreception entity, the scope or spirit of the present invention is notlimited thereto. Similarly, the downlink transmission entity may be a BSor RN and the downlink reception entity may be a UE or RN. In otherwords, uplink transmission may indicate transmission from the UE to theBS, transmission from the UE to the RN, or transmission from the RN tothe BS. Similarly, downlink transmission may indicate transmission fromthe BS to the UE, transmission from the BS to the RN, or transmissionfrom the RN to the UE.

It should be noted that specific terms disclosed in the presentinvention are proposed for the convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, an LTE-Advanced (LTE-A) system,and a 3GPP2 system. In particular, the steps or parts, which are notdescribed to clearly reveal the technical idea of the present invention,in the embodiments of the present invention may be supported by theabove documents. All terminology used herein may be supported by atleast one of the above-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, CDMA (CodeDivision Multiple Access), FDMA (Frequency Division Multiple Access),TDMA (Time Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier Frequency DivisionMultiple Access), and the like. The CDMA may be embodied with wireless(or radio) technology such as UTRA (Universal Terrestrial Radio Access)or CDMA2000. The TDMA may be embodied with wireless (or radio)technology such as GSM (Global System for Mobile communications)/GPRS(General Packet Radio Service)/EDGE (Enhanced Data Rates for GSMEvolution). The OFDMA may be embodied with wireless (or radio)technology such as Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and E-UTRA(Evolved UTRA). The UTRA is a part of the UMTS (Universal MobileTelecommunications System). The 3GPP (3rd Generation PartnershipProject) LTE (long term evolution) is a part of the E-UMTS (EvolvedUMTS), which uses E-UTRA. The 3GPP LTE employs the OFDMA in downlink andemploys the SC-FDMA in uplink. The LTE-Advanced (LTE-A) is an evolvedversion of the 3GPP LTE. WiMAX can be explained by an IEEE 802.16e(WirelessMAN-OFDMA Reference System) and an advanced IEEE 802.16m(WirelessMAN-OFDMA Advanced System). For clarity, the followingdescription focuses on the 3GPP LTE and 3GPP LTE-A system. However,technical features of the present invention are not limited thereto.

FIG. 1 exemplarily shows a radio frame structure for use in a 3rdGeneration Partnership Project Long Term Evolution (3GPP LTE) system. Adownlink (DL) radio frame structure will hereinafter be described withreference to FIG. 1.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) radiopacket communication system, uplink/downlink data packet transmission isperformed in subframe units. One subframe is defined as a predeterminedtime interval including a plurality of OFDM symbols. The 3GPP LTEstandard supports a type 1 radio frame structure applicable to FrequencyDivision Duplex (FDD) and a type 2 radio frame structure applicable toTime Division Duplexing (TDD).

FIG. 1(a) is a diagram showing the structure of the type 1 radio frame.A downlink radio frame includes 10 subframes, and one subframe includestwo slots in a time region. A time required for transmitting onesubframe is defined in a Transmission Time Interval (TTI). For example,one subframe may have a length of 1 ms and one slot may have a length of0.5 ms. One slot may include a plurality of OFDM symbols in a timeregion and include a plurality of Resource Blocks (RBs) in a frequencyregion. Since the 3GPP LTE system uses OFDMA in downlink, the OFDMsymbol indicates one symbol duration. The OFDM symbol may be called anSC-FDMA symbol or a symbol duration. RB is a resource allocation unitand includes a plurality of contiguous carriers in one slot.

The number of OFDM symbols included in one slot may be changed accordingto the configuration of a Cyclic Prefix (CP). The CP includes anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be seven. If the OFDM symbols are configured by the extendedCP, the length of one OFDM symbol is increased, the number of OFDMsymbols included in one slot is less than that of the case of the normalCP. In case of the extended CP, for example, the number of OFDM symbolsincluded in one slot may be six. If the channel state is unstable, forexample, if a User Equipment (UE) moves at a high speed, the extended CPmay be used in order to further reduce interference between symbols.

In case of using the normal CP, since one slot includes seven OFDMsymbols, one subframe includes 14 OFDM symbols. At this time, the firsttwo or three OFDM symbols of each subframe may be allocated to aPhysical Downlink Control Channel (PDCCH) and the remaining OFDM symbolsmay be allocated to a Physical Downlink Shared Channel (PDCCH).

The structure of a type 2 radio frame is shown in FIG. 1(b). The type 2radio frame includes two half-frames, each of which is made up of fivesubframes, a downlink pilot time slot (DwPTS), a guard period (GP), andan uplink pilot time slot (UpPTS), in which one subframe consists of twoslots. That is, one subframe is composed of two slots irrespective ofthe radio frame type. DwPTS is used to perform initial cell search,synchronization, or channel estimation. UpPTS is used to perform channelestimation of a base station and uplink transmission synchronization ofa user equipment (UE). The guard interval (GP) is located between anuplink and a downlink so as to remove interference generated in theuplink due to multi-path delay of a downlink signal. That is, onesubframe is composed of two slots irrespective of the radio frame type.

The structure of the radio frame is only exemplary. Accordingly, thenumber of subframes included in the radio frame, the number of slotsincluded in the subframe or the number of symbols included in the slotmay be changed in various manners.

FIG. 2 is a diagram showing an example of a resource grid in onedownlink slot. OFDM symbols are configured by the normal CP. Referringto FIG. 2, the downlink slot includes a plurality of OFDM symbols in atime region and includes a plurality of RBs in a frequency region.Although one downlink slot includes seven OFDM symbols and one RBincludes 12 subcarriers, the present invention is not limited thereto.Each element of the resource grid is referred to as a Resource Element(RE). For example, a RE a(k,l) is located at a k-th subcarrier and anl-th OFDM symbol. In case of the normal CP, one RB includes 12×7 REs (incase of the extended CP, one RB includes 12×6 REs). Since a distancebetween subcarriers is 15 kHz, one RB includes about 180 kHz in thefrequency region. N^(DL) denotes the number of RBs included in thedownlink slot. The N^(DL) is determined based on downlink transmissionbandwidth set by scheduling of a base station (BS).

FIG. 3 is a diagram showing the structure of a downlink subframe. Amaximum of three OFDM symbols of a front portion of a first slot withinone subframe corresponds to a control region to which a control channelis allocated. The remaining OFDM symbols correspond to a data region towhich a Physical Downlink Shared Channel (PDSCH) is allocated. The basicunit of transmission becomes one subframe. That is, a PDCCH and a PDSCHare allocated to two slots. Examples of the downlink control channelsused in the 3GPP LTE system include, for example, a Physical ControlFormat Indicator Channel (PCFICH), a Physical Downlink Control Channel(PDCCH), a Physical Hybrid automatic repeat request Indicator Channel(PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of asubframe, and includes information about the number of OFDM symbols usedto transmit the control channel in the subframe. The PHICH includes aHARQ ACK/NACK signal as a response of uplink transmission. The controlinformation transmitted through the PDCCH is referred to as DownlinkControl Information (DCI). The DCI includes uplink or downlinkscheduling information or an uplink transmit power control command for acertain UE group. The PDCCH may include resource allocation andtransmission format of a Downlink Shared Channel (DL-SCH), resourceallocation information of an Uplink Shared Channel (UL-SCH), paginginformation of a Paging Channel (PCH), system information on the DL-SCH,resource allocation of an higher layer control message such as a RandomAccess Response (RAR) transmitted on the PDSCH, a set of transmit powercontrol commands for individual UEs in a certain UE group, transmitpower control information, activation of Voice over IP (VoIP), etc. Aplurality of PDCCHs may be transmitted within the control region. The UEmay monitor the plurality of PDCCHs. The PDCCHs are transmitted on anaggregation of one or several contiguous control channel elements(CCEs). The CCE is a logical allocation unit used to provide the PDCCHsat a coding rate based on the state of a radio channel. The CCEcorresponds to a plurality of resource element groups. The format of thePDCCH and the number of available bits are determined based on acorrelation between the number of CCEs and the coding rate provided bythe CCEs. The base station determines a PDCCH format according to a DCIto be transmitted to the UE, and attaches a Cyclic Redundancy Check(CRC) to control information. The CRC is masked with a Radio NetworkTemporary Identifier (RNTI) according to an owner or usage of the PDCCH.If the PDCCH is for a specific UE, a cell-RNTI (C-RNTI) of the UE may bemasked to the CRC. Alternatively, if the PDCCH is for a paging message,a paging indicator identifier P-RNTI) may be masked to the CRC. If thePDCCH is for system information (more specifically, a system informationblock (SIB)), a system information identifier and a system informationRNTI (SI-RNTI) may be masked to the CRC. To indicate a random accessresponse that is a response for transmission of a random access preambleof the UE, a random access-RNTI (RA-RNTI) may be masked to the CRC.

FIG. 4 is a diagram showing the structure of an uplink frame. The uplinksubframe may be divided into a control region and a data region in afrequency region. A Physical Uplink Control Channel (PUCCH) includinguplink control information is allocated to the control region. APhysical uplink Shared Channel (PUSCH) including user data is allocatedto the data region. In order to maintain single carrier characteristics,one UE does not simultaneously transmit the PUCCH and the PUSCH. ThePUCCH for one UE is allocated to a RB pair in a subframe. RBs belongingto the RB pair occupy different subcarriers with respect to two slots.Thus, the RB pair allocated to the PUCCH is “frequency-hopped” at a slotedge.

Carrier Aggregation

Although downlink and uplink bandwidths are different, a wirelesscommunication system typically uses one carrier. For example, a wirelesscommunication system having one carrier for each of the downlink and theuplink and symmetry between the downlink and uplink bandwidths may beprovided based on a single carrier.

The International Telecommunication Union (ITU) requests thatIMT-Advanced candidates support wider bandwidths, compared to legacywireless communication systems. However, allocation of a wide frequencybandwidth is difficult throughout most of the world. Accordingly, atechnology for efficiently using small segmented bands, known as carrieraggregation (bandwidth aggregation) or spectrum aggregation, has beendeveloped in order to aggregate a plurality of physical bands to alogical wider band.

Carrier aggregation was introduced to support increased throughput,prevent a cost increase caused by introduction of wideband RF devices,and ensure compatibility with legacy systems. Carrier aggregationenables data exchange between a UE and an eNB through a group ofcarriers each having a bandwidth unit defined in a legacy wirelesscommunication system (e.g. 3GPP LTE Release-8 or Release-9 in case of3GPP LTE-A). The carriers each having a bandwidth unit defined in thelegacy wireless communication system may be called Component Carriers(CCs) or cells. Carrier aggregation using one or more cells (or CCs) maybe applied to each of the downlink and the uplink. Although one cell (orone CC) supports a bandwidth of 5 MHz, 10 MHz or 20 MHz, carrieraggregation may support a system bandwidth of up to 100 MHz byaggregating up to five cells (or five CCs) each having a bandwidth of 5MHz, 10 MHz or 20 MHz.

Modeling of Multi-Input Multi-Output (MIMO) System

An MIMO system improves data transmission/reception efficiency usingmultiple transmit antennas and multiple receive antennas. In the MIMOtechnology, a single antenna path is not used to receive a wholemessage, that is, whole data may be received by combining a plurality ofpieces of data received through a plurality of antennas.

FIG. 5 is a diagram showing the configuration of a wirelesscommunication system having multiple antennas. As shown in FIG. 5(a), ifthe number of transmit antennas is increased to N_(T) and the number ofreceive antennas is increased to N_(R), a theoretical channeltransmission capacity is increased in proportion to the number ofantennas, unlike the case where a plurality of antennas is used in onlya transmitter or a receiver. Accordingly, it is possible to improve atransfer rate and to remarkably improve frequency efficiency. As thechannel transmission capacity is increased, the transfer rate may betheoretically increased by a product of a maximum transfer rate R₀ uponutilization of a single antenna and a rate increase ratio R_(i).R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For example, in an MIMO system using four transmit antennas and fourreceive antennas, it is possible to theoretically acquire a transferrate which is four times that of a single antenna system. After theincrease in the theoretical capacity of the MIMO system was proved inthe mid-1990s, various technologies of substantially improving a datatransfer rate have been actively developed up to now. In addition,several technologies are already applied to the various radiocommunication standards such as the third-generation mobilecommunication and the next-generation wireless local area network (LAN).

According to the researches into the MIMO antenna up to now, variousresearches such as researches into information theory related to thecomputation of the communication capacity of a MIMO antenna in variouschannel environments and multiple access environments, researches intothe model and the measurement of the radio channels of the MIMO system,and researches into space-time signal processing technologies ofimproving transmission reliability and transmission rate have beenactively conducted.

The communication method of the MIMO system will be described in moredetail using mathematical modeling. In the above system, it is assumedthat N_(T) transmit antennas and N_(R) receive antennas are present.

In transmitted signals, if the N_(T) transmit antennas are present, thenumber of pieces of maximally transmittable information is N_(T). Thetransmitted information may be expressed as follows.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  [Equation 2]

The transmitted information S₁, S₂, . . . , S_(N) _(T) may havedifferent transmit powers. If the respective transmit powers are P₁, P₂,. . . , P_(N) _(T) , the transmitted information with adjusted powersmay be expressed as follows.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P_(N) _(T) s _(N) _(T) ]^(T)  [Equation 3]

In addition, Ŝ may be expressed using a diagonal matrix P of thetransmit powers as follows.

$\begin{matrix}{s = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Considers that the N_(T) actually transmitted signals x₁, x₂, . . . ,x_(N) _(T) are configured by applying a weight matrix W to theinformation vector Ŝ with the adjusted transmit powers. The weightmatrix W serves to appropriately distribute the transmitted informationto each antenna according to a transport channel state, etc. x₁, x₂, . .. , x_(N) _(T) may be expressed by using the vector X as follows.

                                 [Equation  5] $x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1\; N_{T}} \\w_{21} & w_{22} & \ldots & w_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\;\hat{s}} = {W\; P\; s}}}}$

In Equation 5, W_(ij) denotes a weight between an i-th transmit antennaand j-th information. W is also called a precoding matrix.

The transmitted signal x may be differently processed using according totwo schemes (for example, spatial diversity scheme and spatialmultiplexing scheme). In case of the spatial multiplexing scheme,different signals are multiplexed and the multiplexed signal istransmitted to a receiver such that elements of information vector(s)have different values. In case of the spatial diversity scheme, the samesignal is repeatedly transmitted through a plurality of channel pathssuch that elements of information vector(s) have the same value. Acombination of the spatial multiplexing scheme and the spatial diversityscheme may be considered. That is, the same signal may be, for example,transmitted through three transmit antennas according to the spatialdiversity scheme and the remaining signals may be transmitted to thereceiver using the spatial multiplexing scheme.

If the N_(R) receive antennas are present, respective received signalsy₁, y₂, . . . , y_(N) _(R) of the antennas are expressed as follows.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

If channels are modeled in the MIMO radio communication system, thechannels may be distinguished according to transmit/receive antennaindexes. A channel from the transmit antenna j to the receive antenna iis denoted by h_(ij). In h_(ih), it is noted that the indexes of thereceive antennas precede the indexes of the transmit antennas in view ofthe order of indexes.

FIG. 5(b) is a diagram showing channels from the N_(T) transmit antennasto the receive antenna i. The channels may be combined and expressed inthe form of a vector and a matrix. In FIG. 5(b), the channels from theN_(T) transmit antennas to the receive antenna i may be expressed asfollows.h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Accordingly, all the channels from the N_(T) transmit antennas to theN_(R) receive antennas may be expressed as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

An Additive White Gaussian Noise (AWGN) is added to the actual channelsafter a channel matrix H. The AWGN n₁, n₂, . . . , n_(N) _(R) added tothe N_(T) transmit antennas may be expressed as follows.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

Through the above-described mathematical modeling, the received signalsmay be expressed as follows.

                                     [Equation  10]$\mspace{11mu}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1\; N_{T}} \\h_{21} & h_{22} & \ldots & h_{2\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{i\; N_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{H\; x} + n}}}}$

The number of rows and columns of the channel matrix H indicating thechannel state is determined by the number of transmit and receiveantennas. The number of rows of the channel matrix H is equal to thenumber N_(R) of receive antennas and the number of columns thereof isequal to the number N_(T) of transmit antennas. That is, the channelmatrix H is an N_(R)×N_(T) matrix.

The rank of the matrix is defined by the smaller of the number of rowsor columns, which are independent of each other. Accordingly, the rankof the matrix is not greater than the number of rows or columns. Therank rank(H) of the channel matrix H is restricted as follows.rank(H)≦min(N _(T) ,N _(R))  [Equation 11]

In MIMO transmission, the term “rank” denotes the number of paths forindependently transmitting signals, and the term “number of layers”denotes the number of signal streams transmitted through each path. Ingeneral, since a transmitter transmits layers corresponding in number tothe number of ranks used for signal transmission, rank has the samemeaning as the number of layers unless otherwise noted.

In association with the above-mentioned MIMO transmission techniques,the codebook-based precoding method will hereinafter be described withreference to FIG. 6. FIG. 6 is a conceptual diagram illustratingcodebook-based precoding.

In accordance with the codebook-based precoding scheme, a transceivermay share codebook information including a predetermined number ofprecoding matrices according to a transmission rank, the number ofantennas, etc. That is, if feedback information is infinite, theprecoding-based codebook scheme may be used. The receiver measures achannel status through a reception signal, so that an infinite number ofpreferred precoding matrix information (i.e., an index of thecorresponding precoding matrix) may be fed back to the transmitter onthe basis of the above-mentioned codebook information. For example, thereceiver may select an optimum precoding matrix by measuring an ML(Maximum Likelihood) or MMSE (Minimum Mean Square Error) scheme.Although the receiver shown in FIG. 6 transmits precoding matrixinformation for each codeword to the transmitter, the scope or spirit ofthe present invention is not limited thereto.

Upon receiving feedback information from the receiver, the transmittermay select a specific precoding matrix from a codebook on the basis ofthe received information. The transmitter that has selected theprecoding matrix performs a precoding operation by multiplying theselected precoding matrix by as many layer signals as the number oftransmission ranks, and may transmit each precoded Tx signal over aplurality of antennas.

If the receiver receives the precoded signal from the transmitter as aninput, it performs inverse processing of the precoding having beenconducted in the transmitter so that it can recover the reception (Rx)signal. Generally, the precoding matrix satisfies a unitary matrix (U)such as (U*U^(H)=I), so that the inverse processing of theabove-mentioned precoding may be conducted by multiplying a Hermitianmatrix (P^(H)) of the precoding matrix H used in precoding of thetransmitter by the reception (Rx) signal.

SC-FDMA Transmission and OFDMA Transmission

FIG. 7 is a conceptual diagram illustrating an SC-FDMA transmissionscheme and an OFDMA transmission scheme for use in a mobilecommunication system. The SC-FDMA transmission scheme may be used for ULtransmission and the OFDMA transmission scheme may be used for DLtransmission.

Each of the UL signal transmission entity (e.g., UE) and the DL signaltransmission entity (e.g., eNB) may include a Serial-to-Parallel (S/P)Converter 701, a subcarrier mapper 703, an M-point Inverse DiscreteFourier Transform (IDFT) module 704, and a Parallel-to-Serial Converter705. Each input signal that is input to the S/P converter 701 may be achannel coded and modulated data symbol. However, a user equipment (UE)for transmitting signals according to the SC-FDMA scheme may furtherinclude an N-point Discrete Fourier Transform (DFT) module 702. Theinfluence of IDFT processing of the M-point IDFT module 704 isconsiderably offset, such that a transmission signal may be designed tohave a single carrier property. That is, the DFT module 702 performs DFTspreading of an input data symbol such that single carrier propertyrequisite for UL transmission may be satisfied. The SC-FDMA transmissionscheme basically provides good or superior Peak to Average Power ratio(PAPR) or Cubic Metric (CM), such that the UL transmitter can moreeffectively transmit data or information even in the case of the powerlimitation situation, resulting in an increase in user throughput.

Hybrid Automatic Repeat Request (HARQ)

As a control method of data reception failure, the following HARQoperation may be applied. A data transmitter may transmit a new packetif an ACK signal is received from a receiver and retransmit thetransmitted packet if a NACK signal is received, after transmitting onepacket. At this time, the packet subjected to coding with forward errorcorrection (FEC) may be retransmitted. Accordingly, the data receiverreceives and decodes one packet, transmits an ACK signal if decoding issuccessfully performed, transmits a NACK signal if decoding fails, andstores the received packet in a buffer. If the data receiver receivesthe retransmitted packet due to the NACK signal, the data receiverdecodes the retransmitted packet in association with the packet storedin the buffer, thereby increasing a packet reception success rate.

The HARQ scheme may be divided into a synchronous HARQ scheme and anasynchronous HARQ scheme according to retransmission timing. In thesynchronous HARQ scheme, if initial transmission fails, subsequentretransmission is performed at a predetermined time set by a system. Forexample, if retransmission is set to be performed in every fourth timeunit after initial transmission fails, information about aretransmission time does not need to be signaled to the receiver.Accordingly, if the data transmitter receives the NACK signal, thepacket is retransmitted in every fourth time unit until the ACK signalis received. According to the asynchronous HARQ scheme, informationabout a retransmission time is separately scheduled. Accordingly, theretransmission time of the packet corresponding to the NACK signal maybe changed according to various factors such as channel state.

The HARQ scheme may be divided into an adaptive HARQ scheme and anon-adaptive HARQ scheme depending on whether the amount of resourcesused for retransmission is set according to channel state. In thenon-adaptive scheme, a packet modulation scheme, the number of used RBs,etc., which are used upon retransmission, are set in advance uponinitial transmission. For example, if a transmitter transmits data usingeight RBs upon initial transmission, the transmitter also retransmitsdata using eight RBs even upon retransmission. In contrast, in theadaptive scheme, the packet modulation scheme, the number of used RBs,etc. may be changed according to channel state. For example, even whendata is transmitted using eight RBs upon initial transmission,retransmission may be performed using fewer or more than eight RBsaccording to channel state.

A synchronous HARQ scheme is applicable to uplink data transmission of aUE having a single antenna. A HARQ ACK/NACK signal for uplink datatransmission is indicated via a PHICH or a PDCCH among downlink controlchannels. The non-adaptive HARQ scheme may be performed if the PHICH isused and the adaptive HARQ scheme may be performed if the PDCCH is used.

The PHICH is used to transmit 1-bit ACK/NACK information, bit state 0means ACK and bit state 1 means NACK. The 1-bit information is modulatedusing a binary phase shift keying (BPSK) scheme. The non-adaptive schemeis performed if the PHICH is used and a redundancy version (RV) may bechanged according to a predetermined pattern.

The PDCCH is a channel including control information for uplink/downlinkdata transmission. A UE may acquire uplink control information so as toperform uplink data transmission. Downlink control information (DCI) forscheduling uplink transmission may be referred to as uplink (UL) grant.Such control information may include resource allocation information, amodulation and coding scheme (MCS) level, a new data indicator (NDI),power control information, etc. The NDI has a size of 1 bit and has abit state different from a previous NDI bit state if new data is to betransmitted. That is, the NDI value is toggled. In case ofretransmission, control information having the same bit state as the NDIbit of previous control is transmitted. That is, the NDI value is nottoggled. Since the MCS is indicated through the PDCCH, an adaptive HARQscheme is possible.

In the 3GPP LTE system, an uplink HARQ scheme is defined as asynchronous HARQ scheme and a maximum number of retransmissions isconfigured per UE. A downlink ACK/NACK signal responding to uplinktransmission/retransmission is transmitted on a PHICH. An uplink HARQoperation follows the following rules.

1) If a PDCCH indicating a C-RNTI of a UE is accurately receivedregardless of content of HARQ feedback (ACK or NACK), a UE may performan operation indicated by the PDCCH, that is, transmission orretransmission (this may be referred to as adaptive retransmission).

2) If a PDCCH indicating a C-RNTI of a UE is not detected, HARQ feedbackmay indicate a method of performing retransmission by a UE. If HARQfeedback is NACK, the UE performs non-adaptive retransmission. That is,retransmission is performed using the same uplink resources as thosepreviously used by the same HARQ process. If HARQ feedback is ACK, theUE does not perform uplink transmission/retransmission and keeps data ina HARQ buffer. In order to perform retransmission, indication through aPDCCH is required. That is, non-adaptive retransmission is notperformed.

Meanwhile a measurement gap has higher priority than HARQretransmission. That is, if HARQ retransmission collides with ameasurement gap, HARQ retransmission is not performed.

The above-described uplink HARQ operation is summarized as shown inTable 1.

TABLE 1 HARQ feedback PDCCH received received by UE by UE UE behaviorACK or New New transmission is performed according to the NACK trans-PDCCH mission ACK or Re- Retransmission is performed according to theNACK trans- PDCCH (adaptive retransmission) mission ACK NoneTransmission/retransmission is not performed and data is kept in theHARQ buffer. The PDCCH is required to resume retransmission. NACK NoneNon-adaptive retransmission

For detailed description of the uplink HARQ operation, refer to the 3GPPLTE standard (e.g., 3GPP TS 36.300 V8.6.0).

In the conventional 3GPP LTE system (e.g., the 3GPP LTE release 8system), if a multiple antenna transmission scheme is applied to uplinksignal transmission from a UE to a BS, a peak-to-average ratio(PAPR)/cubic metric is deteriorated. Thus, a multiple antennatransmission scheme (MIMO transmission scheme) is defined only indownlink signal transmission from a BS to a UE. Application of amultiple antenna transmission scheme to an uplink signal transmittedfrom a UE to a BS has been discussed for increase in transfer rate anddiversity gain, and a method of applying a multiple antenna transmissionscheme to uplink signal transmission in the subsequent standard (e.g.,3GPP LTE Release-10 or subsequent release, or 3GPP LTE-A) of the 3GPPLTE system has been discussed.

In application of the multiple antenna transmission scheme to uplinksignal transmission, an uplink transmitter (e.g., a UE) may have two orfour transmit antennas. In order to reduce control signal overhead, amaximum of two codewords may be transmitted in uplink. In a system fortransmitting multiple codewords in uplink, an uplink receiver (e.g., aBS) needs to inform the uplink transmitter (e.g., a UE) of detection (ordecoding) success/failure of the codewords. The uplink receiver maytransmit a HARQ ACK/NACK signal of each codeword to the uplinktransmitter. With respect to uplink transmission of two codewords, adetermination as to whether new data transmission or retransmission isperformed depending on whether downlink HARQ feedback received by theuplink transmitter is ACK or NACK may be defined as shown in Table 2.

TABLE 2 First Second codeword codeword Behavior (non-blanking) Behavior(blanking) ACK ACK First codeword: First codeword: new data transmissionnew data transmission Second codeword: Second codeword: new datatransmission new data transmission ACK NACK First codeword: Firstcodeword: new data transmission non-transmission/ Second codeword:retransmission retransmission Second codeword: retransmission NACK ACKFirst codeword: First codeword: retransmission retransmission Secondcodeword: Second codeword: new data transmission non-transmission/retransmission NACK NACK First codeword: First codeword: retransmissionretransmission Second codeword: Second codeword: retransmissionretransmission

In a non-blank operation, new data is transmitted with respect to acodeword for which ACK is received and retransmission is performed withrespect to a codeword for which NACK is received. Meanwhile, in ablanking operation, new data is transmitted with respect to twocodewords if ACK is received with respect to the two codewords, and acodeword for which ACK is received is not transmitted and a codeword forwhich NACK is received is retransmitted if ACK is received with respectto one of the two codewords and NACK is received with respect to theother of the two codewords. If NACK is received with respect to the twocodewords, the two codewords are retransmitted.

Hereinafter, in a HARQ operation for the above-described uplinkmulti-codeword transmission, various embodiments of the presentinvention of a method of configuring control information on a PHICH, aprecoder selection method, a method for selecting PHICH resources, amethod for selecting a DMRS resource, a method of performing the HARQoperation by a UE which receives a PHICH and a PDCCH, and a method ofconfiguring downlink control information (DCI) on a PDCCH will bedescribed.

1. Method of Configuring Control Information on a PHICH for UplinkMultiple-Codeword HARQ Operation

As described above, a HARQ scheme for uplink data transmission issynchronously performed and a PHICH including HARQ ACK/NACK controlinformation for uplink data transmission is transmitted after apredetermined time according to an uplink data transmission period. Anuplink transmitter may determine uplink data retransmission according toan ACK/NACK state indicated by the PHICH. The ACK/NACK state isrepresented by 1 bit and this information is transmitted on a PHICHafter modulation and encoding or modulation and sequence mapping.

Multiple codewords may be used for uplink data transmission. Multiplecodewords may be used for the above-described multiple antennatransmission scheme. Alternatively, multiple codewords may be used for amultiple carrier technique (or a carrier aggregation technique). In thepresent specification, multi-codeword transmission is applicable to amultiple antenna transmission scheme or a multiple carrier technique.

Since 1 bit of information is required to indicate an ACK/NACK state ofone codeword, N bits of information is required to indicate ACK/NACKstates of N codewords. For example, in a system having two codewords, atotal of 2 bits is required to indicate the ACK/NACK states of thecodewords. That is, each of the first and second codewords includes astate of ACK and ACK, a state of ACK and NACK, a state of NACK and ACK,or a state of NACK and NACK. Each state can be represented by 2 bits.N-bit information may be transmitted on a PHICH using various methods.

In Embodiment 1-A, ACK/NACK signals for multiple codewords may bemodulated using a modulation method having an order higher than that ofa conventional BPSK modulation method. For example, ACK/NACK signals oftwo codewords may be represented by 2 bits and 2 bits may be modulatedusing a quadrature phase shift keying (QPSK) scheme. When more bits arerequired to represent the ACK/NACK states as in transmission of two ormore codewords, a modulation scheme such as N-PSK or N-Quadratureamplitude modulation (QAM) may be utilized. If a QPSK scheme is used,points of a total of four states may be represented by 1+j, 1−j, −1−jand −1+j. Alternatively, QPSK may be represented by 1, −1, j and −j. Inthe QPSK scheme, each point may be subjected to power normalization.

In Embodiment 1-B, ACK/NACK signals for multiple codewords may betransmitted on multiple PHICHs. Each PHICH may include 1 bit of ACK/NACKinformation of one codeword. For example, with respect to two codewords,ACK/NACK information may be transmitted on two PHICHs.

In Embodiment 1-C, ACK/NACK signals for multiple codewords may berepresented by 1 bit on one PHICH. Only one of the ACK and NACK signalscan be represented by 1 bit. For example, if two codewords aresuccessfully decoded, ACK is transmitted and, if decoding of any one ofthe two codewords fails, NACK is transmitted. In another example, if anyone of the two codewords is successfully decoded, ACK is transmittedand, if decoding of the two codewords fails, NACK is transmitted.

A method for performing uplink MCW HARQ retransmission according to aPHICH will hereinafter be described in detail.

It is assumed that, under the condition that a PDCCH providing uplinktransmission scheduling information is not detected, a UE can performthe HARQ operation using information indicated by a PHICH. In this case,various embodiments for the MCW retransmission operation in uplink MIMOtransmission will hereinafter be described in detail.

For example, if multiple PHICHs are transmitted with respect to uplinkMCW transmission, a retransmission operation according to an ACK/NACKstate of each codeword may be defined as shown in Table 3. An uplinktransmitter (e.g., a UE) performs retransmission only with respect to acodeword for which NACK is received and does not retransmit a codewordfor which ACK is received. If ACK is received with respect to the twocodewords, the two codewords are not transmitted.

TABLE 3 First Second codeword codeword Uplink transmitter behavior ACKACK First codeword: non-transmission/retransmission (PDCCH is requiredto resume retransmission) Second codeword: non-transmission/retransmission (PDCCH is required to resume retransmission ACK NACKFirst codeword: non-transmission/retransmission (PDCCH is required toresume retransmission) Second codeword: retransmission (non-adaptive)NACK ACK First codeword: retransmission (non-adaptive) Second codeword:non-transmission/ retransmission (PDCCH is required to resumeretransmission NACK NACK First codeword: retransmission (non-adaptive)Second codeword: retransmission (non-adaptive)

In Table 3, no signal is transmitted in a codeword corresponding tonon-transmission/retransmission. That is, a null signal is transmitted.A codeword (CW) having a NACK state transmits a signal, and a codeword(CW) having an ACK state transmits no signal.

The operation of the codeword (or transport block TB) having an ACKstate may be represented by transmission of no signal, or may berepresented by setting of a zero transport block (zero TB).

Meanwhile, if only one of two codewords is retransmitted, precoder powermay be scaled up at a predetermined rate in consideration of the numberof layers mapped to a codeword that does not transmit a signal.

A precoder applied to uplink MCW transmission according to the presentinvention will hereinafter be described in detail.

2. Precoder for Use in Uplink MIMO Transmission

As described above, an uplink MIMO transmission scheme can be applied toa 3GPP LTE-A (LTE Release-10) system, so that uplink transmissionthroughput of the 3GPP LTE-A (LTE Release-10) system can be increased. Ascheme for transmitting multiple transmission streams or multipletransmission layers on a single arbitrary UE for spatial multiplexingmay be used as a technique applicable to UL MIMO transmission. In brief,the above-mentioned scheme can be referred to as a single user MIMO(SU-MIMO) scheme. In the UL SU-MIMO scheme, link adaptation may beapplied to each transmission stream or each transmission stream group. adistinctive modulation and coding scheme (MCS) may be applied for suchlink adaptation. For this purpose, MCW-based transmission can be carriedout in uplink.

The MIMO structure using multiple codewords (MCW) may considersimultaneous transmission of a maximum of two codewords. For such MIMOtransmission, MCS information used by the transmitter, a new dataindicator (NDI) as to whether data to be transmitted is new data orretransmission data, and redundancy version (RV) information as to whichsubpacket is retransmitted in case of retransmission may be needed. MCS,NDI, RV information, etc. may be defined per transport block (TB).

A plurality of transport blocks (TBs) may be mapped to a plurality ofcodewords according to a transport block-to-codeword mapping rule. Forexample, it is assumed that two TBs are represented by TB1 and TB2,respectively, and two codewords are represented by CW0 and CW1,respectively. If two TBs (TB1 and TB2) are activated, the first TB (TB1)may be mapped to a first codeword (CW0) and the second TB (TB2) may bemapped to a second codeword (CW1). Alternatively, TB1 may be mapped toCW1 and TB2 may be mapped to CW0 according to a TB-to-CW swap flag. Onthe other hand, if one of two TBs is deactivated and the other one isactivated, one activated TB may be mapped to the first codeword (CW0).That is, TB and CW may be mapped to each other on a one to one basis. Inaddition, TB deactivation may include an exemplary TB having a size of0. If the size of TB is set to 0, the corresponding TB is not mapped toa codeword.

FIG. 8 is a block diagram illustrating MIMO transmission based onmultiple uplink codewords.

One or more codewords having been encoded by the encoder may bescrambled using a specific scrambling signal. The scrambled codewordsmay be modulated into a complex symbol using BPSK (Binary Phase ShiftKeying), QPSK (Quadrature Phase Shift Keying), or 16QAM or 64QAM(Quadrature Amplitude Modulation). Thereafter, the modulated complexsymbol is mapped to one or more layers. If a signal is transmitted usinga single antenna, one codeword is mapped to one layer and thentransmitted. However, if a signal is transmitted using multipleantennas, the codeword-to-layer mapping relationship as shown in thefollowing tables 4 and 5 is used according to a transmission scheme.

TABLE 4 Number of Number of Codeword-to-layer mapping layers code wordsi = 0, 1, . . . , M_(symb) ^(layer) − 1 1 1 x⁽⁰⁾(i) = d⁽⁰⁾(i) M_(symb)^(layer) = M_(symb) ⁽⁰⁾ 2 2 x⁽⁰⁾(i) = d⁽⁰⁾(i) M_(symb) ^(layer) =M_(symb) ⁽⁰⁾ = x⁽¹⁾(i) = d⁽¹⁾(i) M_(symb) ⁽¹⁾ 2 1 x⁽⁰⁾(i) = d⁽⁰⁾(2i)M_(symb) ^(layer) = M_(symb) ⁽⁰⁾/2 x⁽¹⁾(i) = d⁽⁰⁾(2i + 1) 3 2 x⁽⁰⁾(i) =d⁽⁰⁾(i) M_(symb) ^(layer) = M_(symb) ⁽⁰⁾ = x⁽¹⁾(i) = d⁽¹⁾(2i) M_(symb)⁽¹⁾/2 x⁽²⁾(i) = d⁽¹⁾(2i + 1) 4 2 x⁽⁰⁾(i) = d⁽⁰⁾(2i) M_(symb) ^(layer) =M_(symb) ⁽⁰⁾/2 = x⁽¹⁾(i) = d⁽⁰⁾(2i + 1) M_(symb) ⁽¹⁾/2 x⁽²⁾(i) =d⁽¹⁾(2i) x⁽³⁾(i) = d⁽¹⁾(2i + 1)

TABLE 5 Number Number of code Codeword-to-layer mapping of layers wordsi = 0, 1, . . . , M_(symb) ^(layer) − 1 2 1 x⁽⁰⁾(i) = d⁽⁰⁾(2i) M_(symb)^(layer) = M_(symb) ⁽⁰⁾/2 x⁽¹⁾(i) = d⁽⁰⁾ (2i + 1) 4 1 x⁽⁰⁾(i) = d⁽⁰⁾(4i)x⁽¹⁾(i) = d⁽⁰⁾(4i + 1) x⁽²⁾(i) = d⁽⁰⁾(4i + 2) x⁽³⁾(i) = d⁽⁰⁾(4i + 3)$M_{symb}^{layer} = \left\{ \begin{matrix}{M_{symb}^{(0)}/4} & {{{if}\mspace{14mu} M_{symb}^{(0)}{mod}\mspace{14mu} 4} = 0} \\{\left( {M_{symb}^{(0)} + 2} \right)/4} & {{{if}\mspace{14mu} M_{symb}^{(0)}{mod}\mspace{14mu} 4} \neq 0}\end{matrix} \right.$ If M_(symb) ⁽⁰⁾mod 4 ≠ 0 two null symbols shall beappended to d⁽⁰⁾(M_(symb) ⁽⁰⁾ − 1)

Table 4 shows an exemplary case in which a signal is transmitted usingspatial multiplexing. Table 5 shows an exemplary case in which a signalis transmitted using a transmit diversity scheme. In Tables 4 and 5,x^((a))(i) denotes an i-th symbol of a layer having an index (a), andd^((a))(i) denotes an i-th symbol of a codeword having an index (a). Therelationship of mapping the number of codewords to the number of layerscan be recognized through “Number of layers” of Table 4 and “Number ofcodewords” of Table 5, and a method for mapping symbols of each codewordto a layers can be recognized through the “codeword-to-Layer mapping”item.

As can be seen from Tables 4 and 5, although one codeword can be mappedto one layer in units of a symbol and then transmitted, one codeword maybe distributed and mapped to a maximum of four layers as shown in thesecond case of Table 5. In this way, if one codeword is distributed andmapped to a plurality of layers, it can be recognized that symbolscontained in each codeword are sequentially mapped to individual layersand transmitted. On the other hand, a single encoder block and a singlemodulation block can be used for SCW-based transmission.

As described above, Discrete Fourier Transform (DFT) can be applied to asignal mapped to a layer. In addition, a predetermined precoding matrixcan be multiplied by the layer-mapped signal, and then allocated to eachtransmit antenna. In order to apply predetermined precoding to aDFT-s-OFDMA structure without increasing a transmission PAPR (or CM) ofa UE, the precoding can be performed in a frequency domain aftercompletion of DFT application.

The processed transmission signal for each antenna is mapped totime-frequency resource elements to be used for transmission, and isthen transmitted through each antenna after passing through an OFDMsignal generator.

For correct uplink MIMO transmission, the following processes can beperformed. First of all, a UE transmits a reference signal to a BS, andthe BS can obtain UL spatial channel information from the UE through thereceived reference signal. Based on the obtained spatial channelinformation, the BS selects a rank suitable for UL transmission, obtainsa precoding weight, and calculates channel quality information (CQI).The BS can information the UE of control information for UL signaltransmission. The control information may include UL transmissionresource allocation information, MIMO information (rank, precodingweight, etc.), MCS level, HARQ information (e.g., RV, NDI, etc.), andsequence information for UL DMRS. The UE can transmit a UL signal usingthe above-mentioned control information received from the BS. Controlinformation for UL transmission can be transmitted to a UE through DCIformat fields of a UL grant PDCCH.

Precoding for UL MIMO transmission shown in FIG. 8 will hereinafter bedescribed in detail. The term “precoding” indicates a step for combininga weight vector or a weight matrix with a transmission signal so as totransmit a signal through a spatial channel. Through the precoding blockof FIG. 8, a transmit diversity or long-term beamforming scheme, aprecoded spatial multiplexing scheme, etc. can be implemented. In orderto efficiently support the precoding spatial multiplexing scheme, theprecoding weight can be configured in the form of a codebook. Tables 6to 10 exemplarily illustrate codebooks used for preventing a CM fromincreasing in UL transmission.

Table 6 exemplarily shows the precoding codebook for use in the ULspatial multiplexing transmission scheme using two transmit antennas. Inthe case of using two transmit antennas, one of a total of 6 precodingmatrices may be used for Rank-1 transmission, and one precoding matrixmay be used for Rank-2 transmission.

TABLE 6 Codebook Number of layers υ Index 1 2 0$\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\1\end{bmatrix}$ $\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}$ 1 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- 1}\end{bmatrix}$ 2 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\j\end{bmatrix}$ 3 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\{- j}\end{bmatrix}$ — 4 $\frac{1}{\sqrt{2}}\begin{bmatrix}1 \\0\end{bmatrix}$ 5 $\frac{1}{\sqrt{2}}\begin{bmatrix}0 \\1\end{bmatrix}$

In Table 6, the precoding matrix indicating codebook indexes 4 and 5 forRank-1 transmission can be used as a vector for turning off transmissionthrough a certain antenna so as to cope with an antenna gain imbalance(AGI) situation.

Table 7 shows precoding matrices that are contained in a precodingcodebook having the size of 6 bits applicable to transmission of onelayer (i.e., Rank-1 transmission) in the UL spatial multiplexingtransmission scheme using four transmit antennas. One of a total of 24precoding matrices can be applied to 4-Tx-antenna Rank-1 transmission.

TABLE 7 Codebook Index 0 to 7 $\frac{1}{2}\begin{bmatrix}1 \\1 \\1 \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\1 \\j \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\1 \\{- 1} \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\1 \\{- j} \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\1 \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\j \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\{- 1} \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\j \\{- j} \\{- 1}\end{bmatrix}$ Index  8 to 15 $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\1 \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\j \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\{- 1} \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- 1} \\{- j} \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\1 \\{- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\j \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\{- 1} \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\{- j} \\{- j} \\1\end{bmatrix}$ Index 16 to 23 $\frac{1}{2}\begin{bmatrix}1 \\0 \\1 \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\0 \\{- 1} \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\0 \\j \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 \\0 \\{- j} \\0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\{- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 \\1 \\0 \\{- j}\end{bmatrix}$

The precoding matrices indicated by codebook indexes 16 to 23 shown inTable 7 may be used as a vector for turning off transmission through acertain antenna so as to cope with an antenna gain imbalance (AGI)situation.

Table 8 shows precoding matrices that are contained in a precodingcodebook applicable to transmission of two layers (i.e., Rank-2transmission) in the UL spatial multiplexing transmission scheme using 4Tx antennas. One of a total of 16 precoding matrices can be applied to4-Tx-antenna Rank-2 transmission.

TABLE 8 Codebook Index 0 to 3 $\frac{1}{2}\begin{bmatrix}1 & 0 \\1 & 0 \\0 & 1 \\0 & {- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\1 & 0 \\0 & 1 \\0 & j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- j} & 0 \\0 & 1 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- j} & 0 \\0 & 1 \\0 & {- 1}\end{bmatrix}$ Index 4 to 7 $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- 1} & 0 \\0 & 1 \\0 & {- j}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\{- 1} & 0 \\0 & 1 \\0 & j\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\j & 0 \\0 & 1 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\j & 0 \\0 & 1 \\0 & {- 1}\end{bmatrix}$ Index  8 to 11 $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\1 & 0 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\1 & 0 \\0 & {- 1}\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\{- 1} & 0 \\0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\{- 1} & 0 \\0 & {- 1}\end{bmatrix}$ Index 12 to 15 $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 1 \\1 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & {- 1} \\1 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & 1 \\{- 1} & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 \\0 & 1 \\0 & {- 1} \\{- 1} & 0\end{bmatrix}$

Table 9 shows precoding matrices that are contained in a precodingcodebook applicable to transmission of three layers (i.e., Rank-3transmission) in the UL spatial multiplexing transmission scheme using 4Tx antennas. One of a total of 12 precoding matrices can be applied to4-Tx-antenna Rank-3 transmission.

TABLE 9 Codebook In- dex 0 to 3 $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\{- 1} & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\{- 1} & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ In- dex 4 to 7 $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\1 & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1 \\{- 1} & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\1 & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\{- 1} & 0 & 0 \\0 & 0 & 1\end{bmatrix}$ In- dex 8 to 11 $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1 \\1 & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\1 & 0 & 0 \\0 & 0 & 1 \\{- 1} & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\0 & 0 & 1 \\1 & 0 & 0 \\1 & 0 & 0\end{bmatrix}$ $\frac{1}{2}\begin{bmatrix}0 & 1 & 0 \\0 & 0 & 1 \\1 & 0 & 0 \\{- 1} & 0 & 0\end{bmatrix}$

Table 10 shows precoding matrices that are contained in a precodingcodebook applicable to transmission of four layers (i.e., Rank-4transmission) in the UL spatial multiplexing transmission scheme using 4Tx antennas. Only one precoding matrix can be applied to 4-Tx-antennaRank-4 transmission.

TABLE 10 Codeboook Index 0 $\frac{1}{2}\begin{bmatrix}1 & 0 & 0 & 0 \\0 & 1 & 0 & 0 \\0 & 0 & 1 & 0 \\0 & 0 & 0 & 1\end{bmatrix}$

In the meantime, if transmission of two TBs (or two codewords) isindicated by a UL grant PDCCH, the precoder to be applied to such ULtransmission can be indicated. If the UE transmits two TBs according toa UL grant, a PHICH from the BS can assume that one TB (or one codeword)is successfully decoded (i.e., ACK) and the other TB (or the othercodeword) fails in decoding (i.e., NACK). In this case, a successfullytransmitted transport block TB (or CW) may be set to a zero transportblock, and retransmission of a transport block TB (or CW) having failedtransmission may be attempted. In this case, in association withtransmission of two TBs, the precoder indicated by a UL grant can beapplied to transmission of one TB. That is, the precoder indicated bythe UL grant is selected to transmit multiple TBs (or multiplecodewords). In case of retransmission, one TB (or one CW) is nottransmitted and the other TB (or CW) is transmitted, so that somecolumns from among the precoder indicated by the UL grant can be appliedto data transmission. In other words, data transmission (i.e.,retransmission of the other one TB) can be carried out using only asubset of the precoder indicated by the UL grant.

Embodiment 2-A

In accordance with Embodiment 2-A, the subset of a precoder used forretransmission of a codeword corresponding to NACK can be determined inUL two-codewords transmission.

For example, for Rank-2 UL MIMO transmission using 2 Tx antennas, anidentity matrix shown in FIG. 9(a) may be used. In this case, two TBs(or two CWs) can be transmitted by the UL grant. Assuming that TB1 ismapped to CW1 and TB2 is mapped to CW2, one column of the precoder shownin FIG. 9(a) may be used for CW1 and the other column may be used forCW2. In association with two TBs (or two CWs), if ACK is indicated forone TB (or CW) through a PHICH and NACK is indicated for the other TB(or CW) through a PHICH, only TB (or CW) indicated by NACK can beretransmitted. In case of retransmission, the precoder (for example, theprecoder shown in FIG. 9(a)) indicated by the UL grant can be used. Inthis case, the precoder subset can be used from the viewpoint of aprecoder operation. For example, assuming that TB1 is mapped to CW1 andTB2 is mapped to CW2, only CW2 can be retransmitted if ACK is indicatedfor TB1 and NACK is indicated for TB2. In this case, a value of a secondcolumn acting as the precoder subset shown in FIG. 9(a) can be used forUL data transmission. The above-mentioned operation can be representedby the following equation 12.

$\begin{matrix}{\left. {{\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}\begin{bmatrix}S_{1} \\S_{2}\end{bmatrix}}\rightarrow{{\frac{1}{\sqrt{2}}\begin{bmatrix}1 & 0 \\0 & 1\end{bmatrix}}\begin{bmatrix}0 \\S_{2}\end{bmatrix}} \right. = {{\frac{1}{\sqrt{2}}\begin{bmatrix}0 \\1\end{bmatrix}}S_{2}}} & \left\lbrack {{Equation}\mspace{14mu} 12} \right\rbrack\end{matrix}$

In Equation 12, assuming that a null signal (i.e., 0) is transmitted inone TB (or one CW) from among two UL TBs (or two UL CWs), it is possibleto obtain the same result as in the case in which only a second columnof the precoder is used.

In another example, the matrices shown in FIG. 9(b) can be used forRank-3 UL MIMO transmission through 4 Tx antennas. If transmission oftwo TBs is indicated by the UL grant, two TBs may be mapped to two CWs,respectively. As can be seen from FIG. 9(b), some columns of theprecoder may be used for one CW, and the remaining columns may be usedfor the other CW. In association with two TBs transmitted on uplink, theUE can receive ACK/NACK signals over a PHICH. If ACK is indicated forone certain CW and NACK is indicated for the other one CW, the CW forACK is not transmitted and the CW for NACK can be retransmitted. Even inthe case of retransmission, the precoder (for example, the precoder ofFIG. 9(b)) indicated through the UL grant can be utilized. From theviewpoint of the precoder operation, it can be recognized that theprecoder subset is used. The column mapped to CW used for transmissionis used for UL data transmission. That is, the values of the 2^(nd) and3^(rd) columns acting as the precoder subsets may be used for UL datatransmission. The above-mentioned operation can be represented byEquation 13.

$\begin{matrix}{{{\frac{1}{2}\begin{bmatrix}1 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{bmatrix}}\begin{bmatrix}0 \\S_{2} \\S_{3}\end{bmatrix}} = {{\frac{1}{2}\begin{bmatrix}0 & 0 \\0 & 0 \\1 & 0 \\0 & 1\end{bmatrix}}\begin{bmatrix}S_{2} \\S_{3}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 13} \right\rbrack\end{matrix}$

In Equation 13, assuming that a null signal (i.e., 0) is transmitted inone TB (or one CW) from among two UL TBs (or two UL CWs), it may bepossible to obtain the same result as in the case in which only thesecond and third columns of the precoder are used.

Embodiment 2-B

In accordance with Embodiment 2-B, the precoder used for ULretransmission can be determined.

As described above, the precoder for UL transmission may be indicated bythe UL grant. In this case, information indicating an MCS level for TB(or CW) and information indicating retransmission or new datatransmission may be contained in the UL grant. If multiple TBs (ormultiple CWs) are transmitted, retransmission or new data transmissioncan be performed for the corresponding TB according to NDI indication.

In addition, the UL grant may be identified by HARQ process number.

For example, the precoder indicated by the UL grant (e.g., a UL grantreceived before scheduling initial transmission) having the same HARQprocess number can be used for retransmission.

In other words, assuming that a precoder is used if UL MIMO transmissionis performed without using the UL grant (for example, a UL grant forretransmission is not provided when synchronous non-adaptive HARQretransmission is performed through a PHICH indicating a NACK), theprecoder is indicated by the most recent UL grant from among UL grantshaving the same HARQ process number as the indicated HARQ processnumber.

If UL retransmission is performed using the precoder indicated by themost recent UL grant having the same HARQ process number, and if ACK isreceived for a certain CW and NACK is received for the other CW, the CWcorresponding to ACK can be set to a zero transport block, andretransmission of the CW corresponding to NACK using the precoder subsetmay be attempted.

Embodiment 2-C

In Embodiment 2-C, if ACK/NACK information is received through a PHICHfor UL 2-CW transmission, the following precoder applicable to 1-CWretransmission can be used, and a detailed description thereof willhereinafter be given.

As described above, assuming that two TBs (or two CWs) are transmitted,if one TB (or CW) is successfully decoded and the other one TB (or CW)fails to be decoded, only the TB (or CW) that failed to be decoded canbe retransmitted. It is determined whether decoding success/failure ofthe corresponding TB (or CW) can be confirmed through the ACK or NACKstate for each TB (or CW). In the case of receiving the ACK state for acertain TB (or CW) through a PHICH, the UE does not transmit data of thecorresponding TB (or CW). In the case of receiving the NACK state, theUE transmits data of the corresponding TB (or CW).

The following tables 11 and 12 illustrate examples of UL 2-CWtransmission.

TABLE 11 Time 0 1 2 3 Indication UL Grant PHICH PHICH PHICH Type(NACK|NACK) (NACK|ACK) (ACK) Transmission Initial or Re- Re- No-Trans-Type Re-Tx Transmission Transmission mission Initial or Re- No- Re-TxTransmission Transmission TB TB_1 TB_1 TB_1 transmission TB_2 TB_2 PMIPMI_(time 0) PMI_(time 0) PMI_(time 0) Selection

TABLE 12 Time 0 1 2 Indication UL Grant PHICH PHICH Type (NACK|ACK)(ACK) Transmission Initial or Re Tx Re-Transmission No-Transmission TypeInitial or Re Tx TB TB_1 TB_1 transmission TB_2 PMI Selection PMI_(time0) PMI_(time 0)

Table 11 shows that a UL grant PDCCH is received at a certain time (forexample, a time 0) and initial transmission or retransmission (Re-Tx) of2 TBs (or 2 CWs) is represented by UL grant indication. In this case,the precoder (i.e., PMI_(time 0) indicated by the UL grant can beutilized. If NACK information for 2 TBs (or 2 CWs) that was initiallytransmitted or retransmitted is received through a PHICH at a specifictime (Time 1), both TBs (or CWs) can be retransmitted. At this time, theprecoder to be used may indicate the precoder (i.e., PMI_(time 0))indicated through the most recent uplink grant PDCCH (corresponding to aUL grant received at a time (Time 0)). In association with tworetransmitted TBs (or CWs) (i.e., TB_1 and TB_2), if NACK for TB_1 isreceived through a PHICH and ACK for TB_2 is received through a PHICH ata time 2, TB_1 corresponding to NACK is retransmitted and TB_2corresponding to ACK is not transmitted. At this time, the precoder tobe used may indicate the precoder (i.e., PMI_(time 0)) indicated throughthe most recent uplink grant PDCCH (corresponding to a UL grant receivedat time 0). In association with one retransmitted TB (TB_1), ACK forTB_1 is received through a PHICH at time 3, retransmission is notperformed any longer. If ACK for one retransmitted TB (TB_1) is receivedthrough a PHICH at time 3, retransmission is not performed any longer.

On the other hand, Table 12 shows that a UL grant PDCCH is received at acertain time (e.g., time 0) and two TBs (or two CWs) are initiallytransmitted or retransmitted (Re-Tx) according to UL grant indication.In this case, the precoder (i.e., PMI_(time 0)) indicated by UL grantcan be utilized. In association with two TBs (or two CWs) that wereinitially transmitted or retransmitted, if NACK for TB_1 is receivedthrough a PHICH and ACK for TB_2 is received through a PHICH at a time1, TB_1 corresponding to NACK is retransmitted and TB_2 corresponding toACK is not transmitted. At this time, the precoder to be used mayindicate the precoder (i.e., PMI_(time 0)) indicated through the mostrecent uplink grant PDCCH (corresponding to a UL grant received at time0). In association with one retransmitted TB (TB_1), if ACK is receivedthrough a PHICH at time 2, retransmission is not performed any more.

If retransmission is performed as described above (all of 2 TBs may beretransmitted as shown in the above-mentioned example and only one TBmay also be retransmitted as necessary), the same MCS as in the previoustransmission may be applied to retransmission data (one or two TBs). Inthis case, one physical antenna may have a structure (for example, astructure of a Cubic Metric Preserving Codebook) for transmitting asignal of one layer according to the precoder structure defined for MIMOtransmission. In this case, if one TB (or CW) from among two TBs (or twoCWs) is not transmitted, no signal is transmitted through a physicalantenna corresponding to a layer mapped to non-transmission CW.

Therefore, if another TB (or CW) is not transmitted duringretransmission of a certain TB (or CW) (for example, if ACK for only onefrom among 2 TBs (or 2 Cs) is received), the MIMO scheme must be changedto transmit data through all physical antennas as compared to theprevious transmission. That is, when retransmission of a TB (or CW)indicating NACK is performed by a PHICH, if the MIMO transmission schemeis fallen back using the antenna transmission scheme depending on thenumber of CW-mapped layers (i.e., a rank value), data can be transmittedthrough all physical antennas. Detailed examples of the embodiment 2-Cthat selects a precoding matrix according to the number of layers mappedto one retransmission TB (or CW) will hereinafter be described indetail.

Embodiment 2-C-1

In accordance with Embodiment 2-C-1, when retransmission of a TB (or CW)indicating NACK is performed by a PHICH, if one CW is mapped to onelayer, a single antenna port transmission mode can be applied. A varietyof techniques (for example, cyclic delay diversity (CDD), precodingvector switching (PVS), long-term beamforming, and closed-loop spatialmultiplexing (SM)) in which a single layer is transmitted through aplurality of physical antennas can be applied to the single antenna porttransmission mode.

Alternatively, if one CW is mapped to one layer, the precoder for singlerank transmission can be utilized. The precoder for single ranktransmission may be selected by the UE at random. Otherwise, thepromised precoder between the UE and the BS may be used, and thepromised precoder may be selected as a different precoder at everyretransmission. In another example, the promised precoder may be usedbetween the UE and the BS, and the promised precoder may also beselected as the same precoder at every retransmission. For example, aRank-1 precoder (i.e., a precoder of v=1 shown in Table 6) defined forUL 2Tx antenna transmission of 3GPP LTE Release-10 may be used.Alternatively, a Rank-1 precoder (i.e., the precoder shown in Table 7)defined for UL 4Tx antenna transmission of 3GPP LTE Release-10 may beused.

For example, assuming that 2 TBs (or 2 CWs) are transmitted by a ULgrant PDCCH, if ACK for TB_1 is received through a PHICH and NACK forTB_2 is received through a PHICH, it is assumed that TB_1 is nottransmitted and TB_2 is retransmitted. In this case, UL data isretransmitted according to PHICH information and UL data retransmissioncan be performed through a single layer. That is, one codeword may bemapped to one layer. At this time, a precoding matrix to be used may beused as a precoding matrix for a rank (i.e., Rank-1) corresponding tothe number (=1) of layers mapped to a TB (or CW) indicating NACK.

In other words, assuming that ACK/NACK information for the previouslytransmitted UL data is received through a PHICH, if the number (e.g., 2)of TBs indicated by the most recent PDCCH is different from the number(e.g., 1) of TBs indicated by NACK through a PHICH, the UE performsretransmission of a TB corresponding to NACK. In this case, ULtransmission is performed using the same number of transmission layersas the number of layers (e.g., 1) mapped to a TB (or CW) correspondingto NACK, and the precoding matrix defined for the number (e.g., 1) oftransmission layers may be used. For example, if the number of TBscorresponding to NACK is 1 and a codeword (CW) mapped to thecorresponding TB is mapped to one layer, the Rank-1 precoder may be usedduring retransmission of a TB corresponding to NACK.

Embodiment 2-C-2

In accordance with Embodiment 2-C-2, assuming that retransmission of aTB (or CW) indicated by NACK through a PHICH is performed, if one CW ismapped to two layers, two-antenna-ports transmission mode may be used. Avariety of techniques in which one layer is transmitted through aplurality of physical antennas and the other one layer is transmittedthrough other physical antennas can be applied to the 2-antenna-porttransmission mode.

Alternatively, if one CW is mapped to two layers, the precoder forRank-2 transmission can be utilized. The precoder for Rank-2transmission may be selected by the UE at random. Otherwise, thepromised precoder between the UE and the BS may be used, and thepromised precoder may be selected as a different precoder at everyretransmission. In another example, the promised precoder may be usedbetween the UE and the BS, and the promised precoder may also beselected as the same precoder at every retransmission. For example, aRank-2 precoder (i.e., a precoder of v=2 shown in Table 6) defined forUL 2Tx antenna transmission of 3GPP LTE Release-10 may be used.Alternatively, a Rank-2 precoder (i.e., the precoder shown in Table 8)defined for UL 4Tx antenna transmission of 3GPP LTE Release-10 may beused.

For example, assuming that 2 TBs (or 2 CWs) are transmitted by a ULgrant PDCCH, if ACK for TB_1 is received through a PHICH and NACK forTB_2 is received through a PHICH, it is assumed that TB_1 is nottransmitted and TB_2 is retransmitted. In this case, UL data isretransmitted according to PHICH information and UL data retransmissioncan be performed through two layers. That is, one codeword may be mappedto two layers. At this time, a precoding matrix may be used as aprecoding matrix for a rank (i.e., Rank-2) corresponding to the number(=2) of layers mapped to a TB (or CW) indicating NACK.

In other words, assuming that ACK/NACK information for the previouslytransmitted UL data is received through a PHICH, if the number (e.g., 2)of TBs indicated by the most recent PDCCH is different from the number(e.g., 1) of TBs indicated by NACK through a PHICH, the UE performsretransmission of a TB corresponding to NACK. In this case, ULtransmission is performed using the same number of transmission layersas the number of layers (e.g., 2) mapped to a TB (or CW) correspondingto NACK, and the precoding matrix defined for the number (e.g., 2) oftransmission layers may be used. For example, if the number of TBscorresponding to NACK is 1 and a codeword (CW) mapped to thecorresponding TB is mapped to two layers, the Rank-2 precoder may beused during retransmission of a TB corresponding to NACK.

Embodiment 2-D

Examples of the codeword-to-layer mapping relationship duringretransmission will hereinafter be described with reference toEmbodiment 2-D.

Codeword (CW) swapping will hereinafter be described in detail.

Two codewords are transmitted on uplink, and ACK and NACK, NACK and ACK,or NACK and NACK are received per CW, so that one or two CWs can beretransmitted. In this case, the layer mapped to CW may be greatlychanged as compared to the previous transmission. That is, the layermapped to CW may be changed whenever retransmission is performed.

For example, if NACK for only one of two CWs is received in previoustransmission, the retransmitted (i.e., NACK) CW may be mapped to a layerin which an ACK CW was transmitted in the previous transmission. Forexample, after CW1 is transmitted through a first layer and CW2 istransmitted through a second layer, assuming that ACK for CW1 isreceived and NACK for CW2 is received, CW2 corresponding to NACK isretransmitted. In this case, CW2 is mapped to a first layer and thenretransmitted.

In another example, if NACK for all CWs is received, all CWs areretransmitted. In this case, the position of a layer mapped to CW can bechanged during retransmission. For example, after CW1 is mapped to thefirst layer and CW2 is mapped to the second layer and then transmitted,assuming that NACK is received for both CW1 and CW2, CW1 is mapped tothe second layer and CW2 is mapped to the first layer, so that theresultant CW1 and CW2 can be retransmitted.

Application examples of null-transmission and CW swapping willhereinafter be described in detail.

For example, under the condition that a signal corresponding to a CWhaving received an ACK state is not transmitted (i.e., a null signal istransmitted) and a CW having received a NACK state is retransmitted, theretransmitted CW is mapped to a layer mapped to a CW that has receivedthe ACK state in previous transmission, and then retransmitted. Forexample, after CW1 is transmitted through a first layer and CW2 istransmitted through a second layer, if ACK is received for CW1 and NACKis received for CW2, a null signal is transmitted in association withCW1 and a CW2 corresponding to NACK is retransmitted. In this case, CW2is mapped to the first layer and then retransmitted.

In another example, when a signal corresponding to CW having receivedthe ACK state is not transmitted (i.e., a null signal is transmitted)and only a CW having received the NACK state is retransmitted, theretransmitted CW can be transmitted through a layer different from thelayer mapped in previous transmission. In this case, the position of alayer mapped to a CW may be changed at every retransmission.

In the above-mentioned examples, ACK/NACK information for ULtransmission of two CWs can be obtained through multiple PHICHtransmission (See Embodiment 1-B), or can be obtained through a singlePHICH having multiple states (See Embodiment 1-A).

3. PHICH Resource Allocation for Retransmission

In order to indicate success or failure of TB (or CW) decoding whenmultiple TBs (or CWs) are transmitted, a plurality of PHICH resourcescan be allocated. A plurality of PHICH resources may be allocated sothat ACK/NACK signals of multiple TBs (or CWs) may be indicated.

For example, if a maximum of two TBs (or two CWs) is transmitted onuplink, two PHICH resources can be established, and ACK/NACK informationfor each TB (or CW) may be transmitted through one PHICH resource. PHICHresources may be determined to be a combination of different indexes.For example, a PHICH resource may be established as a combination of thelowest PRB index and the cyclic shift (CS) index that are contained in aDCI format of the UL grant PDCCH. For example, a PHICH resource may beidentified by a pair of indexes (hereinafter referred to as an indexpair) (n_(PHICH) ^(group),n_(PHICH) ^(seq)), wherein n_(PHICH) ^(group)is a PHICH group number, and n_(PHICH) ^(seq) is an orthogonal sequenceindex contained in the corresponding group. n_(PHICH) ^(group) andn_(PHICH) ^(seq) can be defined by the following equation 14.n _(PHICH) ^(group)=(I _(PRB) _(_) _(RA) +n _(DMRS))mod N _(PHICH)^(group) +I _(PHICH) N _(PHICH) ^(group)n _(PHICH) ^(seq)=(└I _(PRB) _(_) _(RA) /N _(PHICH) ^(group) ┘+n_(DMRS))mod 2N _(SF) ^(PHICH)  [Equation 14]

In Equation 14, n_(DMRS) is mapped to TB(s) associated with thecorresponding PUSCH transmission on the basis of ‘CS field for DMRS’(hereinafter referred to as ‘DMRS CS field’) contained in the mostrecent reception PDCCH from among UL grant DCI format PDCCHs (alsocalled a UL DCI format). If the DMRS CS field of a PDCCH having a UL DCIformat is set to ‘000’, n_(DMRS) may be mapped to zero (0). Assumingthat the DMRS CS field is set to ‘001’, ‘010’, ‘011’, ‘100’, ‘101’,‘110’ or ‘111’, n_(DMRS) may be mapped to 1, 2, 3, 4, 5, 6, or 7. On theother hand, assuming that a PDCCH having a UL DCI format for the same TBis not present, if an initial PUSCH for the same TB may besemi-persistently scheduled or an initial PUSCH is scheduled by a randomaccess response grant, n_(DMRS) may be set to zero.

In Equation 14, N_(SF) ^(PHICH) is a spreading factor used for PHICHmodulation.

In Equation 14, I_(PRB) _(_) _(RA) may have any one of I_(PRB) _(_)_(RA) ^(lowest) ^(_) ^(index) or I_(PRB) _(_) _(RA) ^(lowest) ^(_)^(index)+1. I_(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) is the lowest PRBindex of a first slot of the corresponding PUSCH transmission. Anexemplary case in which I_(PRB) _(_) _(RA) is set to I_(PRB) _(_) _(RA)^(lowest) ^(_) ^(index) or I_(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index)+1will hereinafter be described with reference to embodiments of thepresent invention.

In Equation 14, N_(PHICH) ^(group) is the number of PHICH groupsestablished by a higher layer, I_(PHICH) is set to 1 in one case inwhich PUSCH transmission is denoted by n=4 or n=9 at TDD UL/DL setting‘0’, and I_(PHICH) may be set to ‘0’ in the remaining cases.

If transmission of a TB (or CW) indicated by ACK through a PHICH is notperformed, and NDI is toggled at either a UL grant receivedsimultaneously with a PHICH or a UL grant received after PHICHtransmission (i.e., if new data indication is indicated), a flushoperation for acquiring an empty transmission buffer (i.e., if new datatransmission is indicated) can be carried out.

Meanwhile, TB (or CW) indicated by NACK through a PHICH can beretransmitted. In this case, if there is only one TB (or CW) to beretransmitted, information (i.e., ACK/NACK for retransmission) as towhether retransmission is successfully decoded by a receiver can besufficiently represented using only one PHICH resource. That is, afterallocation of multiple PHICH resources, if a certain TB (or CW) fromamong multiple TBs (or CWs) indicates ACK and another TB (or CW)indicates NACK, retransmission can be performed. In the case ofretransmission, a PHICH suitable for the number of TBs (or CWs)participating in retransmission can be used.

For example, assuming that two PHICH resources are allocated for two TBs(or two CWs), if one of two TBs (or two CWs) indicates ACK and the otherone TB (or CW) indicates NACK through two PHICH resources,retransmission of one TB (or CW) indicated by NACK is attempted. In caseof retransmission, one PHICH resource is used for one TB (or CW) to beretransmitted, so that ACK or NACK for the corresponding TB (or CW) canbe indicated.

Assuming that multiple PHICH resources are used for UL MCW transmission,if ACK for some TBs is received through the multiple PHICH resources andNACK for some other TBs is received through the multiple PHICHresources, retransmission of a TB corresponding to NACK is performed.PHICH resources indicating ACK/NACK for such retransmission may beselected as some resources from among multiple PHICH resources. Examplesfor selecting PHICH resources will hereinafter be described.

Embodiment 3-A

In accordance with Embodiment 3-A, PHICH resources allocated for a firstTB (or CW) can be allocated as PHICH resources for retransmission.

For example, it may be assumed that UL transmission of two TBs throughthe UL grant PDCCH is scheduled. That is, a PDCCH may indicate initialtransmission of two TBs. Therefore, the UE may transmit two TBs througha PUSCH. In association with two UL transmission TBs, ACK/NACKinformation may be received through multiple PHICH resources. Forexample, in order to indicate ACK/NACK information of the first TB, afirst PHICH resource can be allocated. In order to indicate ACK/NACKinformation of the second TB, a second PHICH resource can be allocated.The first PHICH resource and the second PHICH resource may bedistinguished from each other according to different indexes. Forexample, if the lowest PRB index (I) is allocated to the first PHICHresource, the lowest PRB index (I+1) may be allocated to the secondPHICH resource.

If a PHICH indicates a NACK of one TB (i.e., first TB or second TB) fromamong two UL transmission TBs, retransmission of a TB corresponding toNACK can be performed. Such retransmission is performed through a PUSCH.In this case, the UL grant PDCCH that directly schedules thecorresponding PUSCH transmission is not present, and retransmission canbe performed using an MCS level contained in the most recent PDCCH (forexample, a PDCCH that schedules initial transmission of 2 TBs). Inassociation with retransmission of a TB corresponding to NACK, ACK/NACKinformation can be received through a PHICH. In this case, a PHICHresource for retransmission of a TB corresponding to NACK can beselected as a PHICH resource (i.e., a first PHICH resource) allocatedfor the first TB from among multiple PHICH resources.

In other words, provided that a PDCCH related to transmission of acertain PUSCH is not present (i.e., if retransmission is performedaccording to PHICH reception without using the UL grant PDCCH), if thenumber (for example, 1 in the aforementioned example) of TBs indicatedby NACK is different from the number (for example, 2 in theaforementioned example) of TBs indicated by the most recent PDCCH (i.e.,a PDCCH that schedules initial transmission of two TBs in theaforementioned example) related to the corresponding PUSCH (i.e., PUSCHthat retransmits a TB indicating a NACK), a PHICH resource (i.e., afirst PHICH resource) allocated for the first TB can be selected as aPHICH resource indicating ACK/NACK information related to retransmissionof a TB indicating NACK. For example, assuming that any one of the firstTB and the second TB indicates NACK during previous transmission, aPHICH resource allocated for retransmission of the NACK TB may beestablished as a PHICH resource (i.e., a first PHICH resource) for thefirst TB, irrespective of whether the NACK TB is the first TB or thesecond TB. For example, if I_(PRB) _(_) _(RA) shown in Equation 14 maybe established as I_(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index) inassociation with the first TB of a PUSCH, or if the number of NACK TBsis different from the number of TBs indicated by the most recent PDCCHrelated to the corresponding PUSCH so that no related PDCCH exists,I_(PRB) _(_) _(RA) may be set to I_(PRB) _(_) _(RA) ^(lowest) ^(_)^(index). In addition, I_(PRB) _(_) _(RA) shown in Equation 14 may beestablished as I_(PRB) _(_) _(RA) ^(lowest) ^(_) ^(index)+1 inassociation with the second TB of a PUSCH having a related PDCCH.

Embodiment 3-B

In accordance with Embodiment 3-B, the same PHICH resource as a PHICHresource that has been allocated for each TB (or CW) in previoustransmission can be allocated to retransmission of each TB (or CW).

For example, during the previous transmission, ACK/NACK information canbe transmitted through a first PHICH resource in association with thefirst TB (or CW), and ACK/NACK information can be transmitted through asecond PHICH resource in association with the second TB (or CW). If ACKis received for the first TB (or CW) and NACK is received for the secondTB (or CW), retransmission of the second TB (or CW) corresponding toNACK is performed, and the first TB (or CW) corresponding to ACK may notbe transmitted. In this case, ACK/NACK information for the second TB (orCW) to be retransmitted can be transmitted through the same PHICHresource as in the previous transmission.

Embodiment 3-C

In accordance with Embodiment 3-C, from among PHICH resources allocatedto each TB (or CW) during previous transmission, a PHICH resourceallocated for each TB (or CW) having either a high MCS or the same MCScan be allocated for TB (or CW) retransmission.

For example, during the previous transmission, ACK/NACK information canbe transmitted through a first PHICH resource in association with thefirst TB (or CW), and ACK/NACK information can be transmitted through asecond PHICH resource in association with the second TB (or CW). In thiscase, it is assumed that the first TB has an MCS higher than that of thesecond TB. If ACK is received for the first TB (or CW) and NACK isreceived for the second TB (or CW), retransmission of the second TB (orCW) corresponding to NACK is performed, and the first TB (or CW)corresponding to ACK may not be transmitted. In this case, ACK/NACKinformation for the second TB (or CW) to be retransmitted can betransmitted through a PHICH resource (i.e., the first PHICH resource)allocated for the first TB having a high MCS. Alternatively, a PHICHresource allocated for a TB having the same MCS as an MCS level of aretransmission TB from among TBs of the previous transmission can beallocated to the retransmission TB.

Embodiment 3-D

In accordance with Embodiment 3-D, from among PHICH resources allocatedto each TB (or CW) in previous transmission, a PHICH resource allocatedfor a TB (or CW) having a low MCS or the same MCS can be allocated forTB (or CW) retransmission.

For example, during the previous transmission, ACK/NACK information canbe transmitted through a first PHICH resource in association with thefirst TB (or CW), and ACK/NACK information can be transmitted through asecond PHICH resource in association with the second TB (or CW). In thiscase, it is assumed that the first TB has an MCS lower than that of thesecond TB. If ACK is received for the first TB (or CW) and NACK isreceived for the second TB (or CW), retransmission of the second TB (orCW) corresponding to NACK is performed, and the first TB (or CW)corresponding to ACK may not be transmitted. In this case, ACK/NACKinformation for the second TB (or CW) to be retransmitted can betransmitted through a PHICH resource (i.e., the first PHICH resource)allocated for the first TB having a low MCS. Alternatively, a PHICHresource allocated for a TB having the same MCS as an MCS level of aretransmission TB from among TBs of the previous transmission can beallocated to the retransmission TB.

4. RS Resource Allocation

For UL transmission, a demodulation reference signal (DMRS) can betransmitted. DMRS is a reference signal that is adapted to perform ULchannel estimation for each antenna port or for each layer.

A cyclic shift (CS) value may be adapted to generate a DMRS sequence. ACS index applied to UL DMRS may be indicated through the ‘Cyclic shiftfor DMRS’ field of a PDCCH DCI format. In case of multi-layer channelestimation, UL DMRSs can be isolated from each other using the CS sothat the UL DMRSs can be multiplexed. That is, each DMRS can be appliedto each UL layer, and different DMRSs can be distinguished from eachother on the basis of different CS indexes. That is, the CS may beconsidered to be an orthogonal resource for discriminating a DMRS. Inaddition, as the distance between CS resources applied to a DMRS foreach layer is increased, performance of discriminating each layer by thereceiver may be increased.

For example, a PUSCH DMRS sequence r_(PUSCH) ^((λ))(•) for a layer λε{0,1, . . . , υ−1} may be defined as r_(PUSCH) ^((λ))(m·M_(sc)^(RS)+n)=w^((λ))(m)r_(u,v) ^((α) ^(λ) ⁾(n) where, m=0, 1, n=0, . . . ,M_(sc) ^(RS)−1 and M_(sc) ^(RS)=M_(sc) ^(PUSCH). For example, anorthogonal sequence w^((λ))(m) may be given as [w^(λ)(0) w^(λ)(1)]=[11], or may be defined using the cyclic shift (CS) field (i.e., a cyclicshift index field for DMRS) indicated by a DCI format related to themost recent uplink for a TB related to the corresponding PUSCHtransmission. For example, assuming that the CS field of a DCI format isset to ‘000’, [w^((λ))(0) w^((λ))(1)] may be set to [1 1], [1 1], [1 −1]and [1 −1] in association with λ=0, λ=1, λ=2 and λ=3, respectively. Inaddition, if the CS field of a DCI format is set to ‘001’, [w^((λ))(0)w^((λ))(1)] may be set to [1 −1], [1 −1], [1 1] and [1 1] in associationwith λ=0, λ=1, λ=2 and λ=3, respectively. If the CS field of a DCIformat is set to ‘010’, [w^((λ))(0) w^((λ))(1)] may be set to [1 −1], [1−1], [1 1] and [1 1] in association with λ=0, λ=1, λ=2 and λ=3,respectively. If the CS field of a DCI format is set to ‘011’,[w^((λ))(0) w^((λ))(1)] may be set to [1 1], [1 1], [1 1] and [1 1] inassociation with λ=0, λ=1, λ=2 and λ=3, respectively. If the CS field ofa DCI format is set to ‘100’, [w^((λ))(0) w^((λ))(1)] may be set to [11], [1 1], [1 1] and [1 1] in association with λ=0, λ=1, λ=2 and λ=3,respectively. If the CS field of a DCI format is set to ‘101’,[w^((λ))(0) w^((λ))(1)] may be set to [1 −1], [1 −1], [1 −1] and [1 −1]in association with λ=0, λ=1, λ=2 and λ=3, respectively. If the CS fieldof a DCI format is set to ‘110’, [w^((λ))(0) w^((λ))(1)] may be set to[1 −1], [1 −1], [1 −1] and [1 −1] in association with λ=0, λ=1, λ=2 andλ=3, respectively. If the CS field of a DCI format is set to ‘111’,[w^((λ))(0) w^((λ))(1)] may be set to [1 1], [1 1], [1 −1] and [1 −1] inassociation with λ=0, λ=1, λ=2 and λ=3, respectively.

In addition, in case of r_(PUSCH) ^((λ))(m·M_(sc)^(RS)+n)=w^((λ))(m)r_(u,v) ^((α) ^(λ) ⁾(n), a cyclic shift (CS) of aslot n_(s) is given as α_(λ)=2πn_(cs,λ)/12, and is defined asn_(cs,λ)=(n_(DMRS) ⁽¹⁾+n_(DMRS,λ) ⁽²⁾+n_(PN)(n_(s)))mod 12. In thiscase, n_(DMRS) ⁽¹⁾ may be set to 0, 2, 3, 4, 6, 8, 9 or 10 when aparameter (cyclicShift) provided by a higher layer is set to 0, 1, 2, 3,4, 5, 6 or 7. In addition, n_(DMRS,λ) ⁽²⁾ is determined by the ‘cyclicshift for DMRS’ field indicated by the most recent uplink DCI format ofa transport block (TB) related to the corresponding PUSCH transmission.

For example, assuming that the CS field of a DCI format is set to ‘000’,n_(DMRS,λ) ⁽²⁾ may be set to 0, 6, 3 and 9 in association with λ=0, λ=1,λ=2 and λ=3, respectively. In addition, if the CS field of a DCI formatis set to ‘001’, n_(DMRS,λ) ⁽²⁾ may be set to 6, 0, 9 and 3 inassociation with λ=0, λ=1, λ=2 and λ=3, respectively. If the CS field ofa DCI format is set to ‘010’, n_(DMRS,λ) ⁽²⁾ may be set to 3, 9, 6 and 0in association with λ=0, λ=1, λ=2 and λ=3, respectively. If the CS fieldof a DCI format is set to ‘011’, n_(DMRS,λ) ⁽²⁾ may be set to 4, 10, 7and 1 in association with λ=0, λ=1, λ=2 and λ=3, respectively. If the CSfield of a DCI format is set to ‘100’, n_(DMRS,λ) ⁽²⁾ may be set to 2,8, 5 and 11 in association with λ=0, λ=1, λ=2 and λ=3, respectively. Ifthe CS field of a DCI format is set to ‘101’, n_(DMRS,λ) ⁽²⁾ may be setto 8, 2, 11 and 5 in association with λ=0, λ=1, λ=2 and λ=3,respectively. If the CS field of a DCI format is set to ‘110’,n_(DMRS,λ) ⁽²⁾ may be set to 10, 4, 1 and 7 in association with λ=0,λ=1, λ=2 and λ=3, respectively. If the CS field of a DCI format is setto ‘111’, n_(DMRS,λ) ⁽²⁾ may be set to 9, 3, 0 and 6 in association withλ=0, λ=1, λ=2 and λ=3, respectively.

When transmitting a DMRS on uplink, a signal generated in a time domainfor use in the uplink data part is converted into a frequency-domainsignal through DFT processing, and is mapped to subcarriers. Thereafter,IFFT processing and CP attachment of the subcarrier mapping result areconducted and transmitted (See FIG. 7), DFT processing of a DMRS isomitted, the DMRS is directly generated in a frequency domain and ismapped to subcarriers, and IFFT processing and CP attachment of thesubcarrier mapping result are conducted and transmitted. In addition,the position of an OFDM symbol mapped to a DMRS in a UL subframe is asfollows. In case of a normal CP, a DMRS is located at a fourth OFDMsymbol of each of the two slots within one subframe. In case of anextended CP, a DMRS is located at a third OFDM symbol of each of the twoslots within one subframe.

As described above, when transmitting two TBs (or two CWs), a sequencecalculated on the basis of a CS index indicated by a DCI format of themost recent reception PDCCH can be applied to a DMRS. If decoding of oneof two TBs (or two CWs) is successfully performed and decoding of theother one TB (or CW) fails, retransmission of one TB (or CW) havingfailed to be decoded can be performed. In this case, for retransmissionof one TB (or CW) having failed decoding, there is a need to definewhich CS index is to be used. If a CS index to be used for thetransmitter and the receiver is not determined, it may be impossible toperform channel estimation of a layer.

Therefore, when the UE performs the HARQ operation using informationindicated by a PHICH under the condition that a PDCCH providingscheduling information of UL transmission is not detected,retransmission of some TBs (or CWs) can be performed. In this case, itmay be necessary to determine whether a CS allocated to UL multiplelayers is to be allocated as in the previous transmission, or it may benecessary to determine whether a new CS is to be allocated so as toincrease the distance of CS resources. CS resource allocation accordingto embodiments of the present invention will hereinafter be described.

Embodiment 4-A

Considering the CW-to-layer mapping relationship shown in Tables 4 and5, one certain CW can be mapped to a specific layer (one or morelayers). When a certain TB (or CW) is retransmitted, a CS indexallocated for a layer mapped to the retransmitted CW can be used for thecorresponding retransmission.

For example, it is assumed that CW1 is mapped to a first layer and CW2is mapped to second and third layers, so that the mapped results can betransmitted. If ACK is received in association with CW1 and NACK isreceived in association with CW2, CW2 corresponding to NACK can beretransmitted. In this case, the layer mapped to the retransmitted CW2can be newly determined according to the CW-to-layer mapping rule. Forexample, the retransmitted CW2 can be mapped to the first and secondlayers. In this case, using the CS index allocated for the layers (i.e.,the first and second layers) mapped to the retransmitted CW2, a sequencefor a DMRS of a layer used for retransmission can be generated.

In other words, the layer mapped to the retransmitted CW can be resetaccording to the CW-to-layer mapping rule during retransmission of a CWindicating a NACK. In accordance with Embodiment 4-A, the CS index forDMRS for use in retransmission may be represented by a CS index for alayer that is newly mapped (reset) to the retransmitted CW. For example,the CS value n_(DMRS,λ) ⁽²⁾ for a DMRS can be determined according tonot only ‘CS index for DMRS’ indicated by the UL grant PDCCH but alsothe number (i.e., rank) of layers of a transmission signal. Theoperation for resetting the layer mapped to the retransmitted CWaccording to the codeword-to-layer mapping rule during retransmission ofa CW corresponding to NACK may also indicate that the DMRS CS valuen_(DMRS,λ) ⁽²⁾ is (newly) re-determined according to not only the ‘CSindex for DMRS’ field indicated by the most recent UL grant DCI formatPDCCH but also the number of layers attempting retransmission.

Embodiment 4-B

If some TBs (or CWs) are retransmitted for UL MCW transmission, aprecoder subset (or some columns) indicated by the most recent UL grantPDCCH can be selected (See Embodiment 2). In this case, the precoder canalso be used for mapping the layer to antenna ports. Therefore, if somecolumns of the precoder are selected in retransmission, this means thatsome layers from among layers mapped to the precoder are selected.Accordingly, as a CS index for a DMRS used for retransmission, a CSindex allocated for the layer selected by the precoder can be utilized.

For example, it is assumed that CW1 is mapped to a first layer and CW2is mapped to second and third layers so that the mapped results can betransmitted. If ACK is received in association with CW1 and NACK isreceived in association with CW2, CW2 corresponding to NACK can beretransmitted. For example, during CW2 retransmission, second and thirdcolumns of the precoder can be selected as the precoder subsets of FIG.9(b). That is, the second and third columns of the precoder can beselected for CW2 retransmission, so that the second and third layers canbe selected. Accordingly, using the CS index allocated for the layers(i.e., the second and third layers) corresponding to the precodercolumns used for retransmission, a sequence for a DMRS of a layer usedfor retransmission can be generated.

In other words, the precoder subset selected by retransmission of a NACKCW may indicate the layer mapped to the retransmitted CW in previoustransmission. In accordance with Embodiment 4-B, the CS index for DMRSfor use in retransmission may be represented by reuse of a CS index thatwas used for the layer mapped to the corresponding CW in previoustransmission. For example, the CS value n_(DMRS,λ) ⁽²⁾ for a DMRS can bedetermined according to not only ‘CS index for DMRS’ indicated by the ULgrant PDCCH but also the number (i.e., rank) of layers of a transmissionsignal. In association with the CS index for DMRS during retransmissionof NACK CW, reuse of the CS index that was used for the layer mapped tothe corresponding CW in previous transmission may also indicate that theCS value n_(DMRS,λ) ⁽²⁾ of a DMRS having been allocated for TB1 or TB2in the previous transmission is used for the layer corresponding to a TBattempting retransmission. Here, in case of TB1 retransmission, the TBattempting retransmission is identical to a TB1 of the previoustransmission, and in case of TB2 retransmission, the TB attemptingretransmission is identical to a TB2 of the previous transmission.

5. HARQ Operations Based on PHICH and PDCCH

As described above, the UL HARQ operation of a UE can be defined indifferent ways according to one case in which the UE does not detect theUL grant PDCCH and uses information indicated through a PHICH, and theother case in which the UE performs PHICH transmission and detects a ULgrant PDCCH.

In accordance with Embodiment 4-B, when the HARQ operation is performedon the condition that the UE detects a PDCCH, a method forretransmitting multiple TBs (or CWs) in UL MIMO transmission willhereinafter be described in detail.

Embodiment 5-A

In accordance with Embodiment 5-A, in association with UL MCWtransmission, ACK/NACK information received through a PHICH is combinedwith control information received through a PDCCH so that it can bedetermined whether the UE will perform retransmission or new datatransmission.

It is assumed that a PHICH can indicate ACK/NACK states for each TB (orCW). That is, multiple PHICHs can be provided to multiple TBs (or CWs),or one PHICH can provide an ACK/NACK state for each TB (or CW) throughmultiple states (See Embodiments 1-A and 1-B).

Control information provided through a PDCCH may include a new dataindicator (NDI). In this case, in association with transmission of 2 TBs(or 2 CWs), an ACK/NACK state indicated by a PHICH is combined with anNDI state through a PDCCH, so that the UE operation can be determinedaccording to the combination result. Alternatively, another fieldinstead of an NDI of a PDCCH, may also be used as necessary.

The UE may receive a PHICH at a predetermined time (for example, afterlapse of four subframes) upon completion of UL 2CW transmission, mayreceive a PDCCH while simultaneously receiving a PHICH, or may receive aPDCCH at a specific time after PHICH reception.

In this case, the UE operation can be represented by the followingequation 13.

TABLE 13 PHICH ACK/NACK PDCCH state seen by the UE UE Behavior 1^(st)ACK or New transmission New transmission according to CW NACK PDCCH ACKor Retransmission Retransmission according to NACK PDCCH (adaptiveretransmission) 2^(nd) ACK or New transmission New transmissionaccording to CW NACK PDCCH ACK or Retransmission Retransmissionaccording to NACK PDCCH (adaptive retransmission)

If the UE can view PDCCH control information, the HARQ operation to beperformed by the UE can be designated by PDCCH indication. If a PDCCHindicates new data transmission of a certain TB (or CW) (for example, ifan NDI value is toggled), the UE may empty the HARQ buffer and mayattempt new data transmission. In other words, if retransmission or newtransmission of each TB (or CW) is indicated through a PDCCH, the HARQoperation can be performed according to PDCCH indication withoutconsidering ACK/NACK states for each TB (or CW) indicated by a PHICH.

Hereinafter, an exemplary case in which only one of two TBs (or two CWs)is transmitted and the other one TB (or CW) is not transmitted (or if anull signal is transmitted) according to the embodiments of the presentinvention will be described in detail.

By combining an ACK/NACK state of each TB (or CW) indicated by a PHICHwith a predetermined indicator (for example, NDI) indicatingretransmission or new transmission of each TB (or CW), it is possible toinform the UE of which TB (or CW) is not transmitted.

For example, a TB (or CW) indicating ACK through a PHICH may indicatethat retransmission is not performed. In this case, if an indicator(e.g., NDI) contained in a PDCCH does not indicate new transmission ofthe corresponding TB (or CW) (for example, if NDI is not toggled), thecorresponding TB (or CW) is not transmitted. That is, the correspondingTB (or CW) is disabled. Alternatively, if an indicator (e.g., NDI)contained in a PDCCH indicates new transmission of the corresponding TB(or CW) (for example, if NDI is toggled), new data transmission of thecorresponding TB (or CW) is performed.

In the meantime, a TB (or CW) indicated by NACK through a PHICHindicates execution of retransmission. In this case, if an indicator(e.g., NDI) contained in a PDCCH does not indicate new transmission ofthe corresponding TB (or CW) (that is, if NDI is not toggled),retransmission of the corresponding TB (or CW) can be performed.

In association with a TB (or CW) indicated by NACK through a PHICH, ifan indicator (e.g., NDI) contained in a PDCCH indicates new transmission(e.g., if NDI is toggled), there occurs ambiguity as to whetherretransmission or new data transmission is performed. Under thissituation, no transmission of the corresponding TB (or CW) may beestablished (that is, the corresponding TB (or CW) is disabled).Alternatively, new data may be transmitted at the corresponding TB (orCW) on the basis of a PDCCH indicator.

In brief, the UE operation determined by a combination of PHICHinformation of one TB (or CW) with PDCCH information can be representedby the following tables 14 and 15.

TABLE 14 PHICH ACK/NACK state PDCCH indicator state UE Behavior 1^(st)CW ACK New-Transmission X No transmission (or 2^(nd) ACKNew-Transmission O New data transmission CW) NACK New-Transmission XRe-transmission NACK New-Transmission O No transmission

TABLE 15 PHICH ACK/NACK state PDCCH indicator state UE Behavior 1^(st)CW ACK New-Transmission X No transmission (or 2^(nd) ACKNew-Transmission O New data transmission CW) NACK New-Transmission XRe-transmission NACK New-Transmission O New data transmission

Embodiment 5-B

In accordance with Embodiment 5-B, in association with UL MCWtransmission, ACK/NACK information through a single PHICH is combinedwith control information through a PDCCH so that it can be determinedwhether the UE will perform retransmission or new data transmission.

In this case, it is assumed that only one of an ACK state and a NACKstate for multiple TBs (or CWs) is indicated through a single PHICH (SeeEmbodiment 1-C). For example, an ACK/NACK signal for multiple TBs (orCWs) can be represented by 1 bit on a single PHICH. If two TBs (or twoCWs) are successfully decoded, ACK can be indicated. If at least one oftwo TBs (or two CWs) fails to decode, NACK can be indicated.

If a single PHICH is transmitted as described above, the UE operationdepending upon an ACK/NACK state indicated by a PHICH can be representedby the following table 16.

TABLE 16 1^(st) and 2^(nd) CW Behavior ACK 1^(st) CW:Non-(Re)transmission (PDCCH is required to resume retransmission) 2^(nd)CW: Non-(Re)transmission (PDCCH is required to resume retransmission)NACK 1^(st) CW: Retransmission (Non-adaptive) 2^(nd) CW: Retransmission(Non-adaptive)

With reference to Table 16, in association with two TBs (or two CWs), ifa PHICH indicates the ACK state, two TBs (or two CWs) are nottransmitted at all, and UL scheduling caused by a PDCCH is required forretransmission. In the meantime, in association with two TBs (or twoCWs), if a PHICH indicates a NACK state, non-adaptive retransmission ofall the TBs (or CWs) can be performed.

If control information provided through a PDCCH may include an NDI, theUE operation for transmission of 2 TBs (or 2 CWs) can be determined bycombining an ACK/NACK state indicated by a PHICH with an NDI stateobtained through a PDCCH. Alternatively, another field instead of an NDIof a PDCCH may be used as necessary.

The UE may receive a PHICH at a predetermined time (for example, afterlapse of four subframes) upon completion of UL 2CW transmission, mayreceive a PDCCH while simultaneously receiving a PHICH, or may receive aPDCCH at a specific time after PHICH reception. In this case, one PHICHmay indicate an ACK or NACK state of two TBs (or two CWs), and anindicator for each TB (or CW) may be contained in a PDCCH. In this case,the UE operation can be represented by the following table 17.

TABLE 17 PHICH ACK/NACK PDCCH state seen by the UE UE Behavior 1^(st)ACK New transmission New transmission according to CW PDCCH and ACKRetransmission Retransmission according to 2^(nd) PDCCH CW (adaptiveretransmission) NACK New transmission New transmission according toPDCCH NACK Retransmission Retransmission according to PDCCH (adaptiveretransmission)

If the UE can view PDCCH control information, the HARQ operation to beperformed by the UE can be designated by PDCCH indication. If a PDCCHindicates new data transmission of a certain TB (or CW) (for example, ifan NDI value is toggled), the UE may empty the HARQ buffer and mayattempt new data transmission. In other words, if retransmission or newtransmission of each TB (or CW) is indicated through a PDCCH, the HARQoperation can be performed according to PDCCH indication withoutconsidering ACK/NACK states for two TBs (or two CWs) indicated by asingle PHICH.

Hereinafter, an exemplary case in which an ACK or NACK state for two TBs(or two CWs) is indicated through a single PHICH under the conditionthat the UE detects a PDCCH according to the present invention will bedescribed in detail.

Retransmission or new data transmission of the UE for each TB (or CW)can be determined by combining a single PHICH ACK/NACK state with apredetermined indicator (for example, NDI) indicating retransmission ornew data transmission for each TB (or CW) contained in a PDCCH. Detailedexamples will hereinafter be described with reference to the followingtables 18 and 19.

TABLE 18 PHICH ACK/NACK Indicator for Indicator for state 1st CW 2nd CWBehavior ACK New New New data transmission transmission transmission ACKNew Retransmission 1st CW: New data transmission transmission 2nd CW:Retransmission ACK Retransmission New 1st CW: Retransmissiontransmission 2nd CW: New data transmission NACK RetransmissionRetransmission Retransmission

For example, an indicator shown in Table 18 may be an NDI contained in aUL grant PDCCH. As can be seen from Table 18, if an ACK state isreceived through a single PHICH and new transmission is indicatedthrough a PDCCH indicator, it is possible to attempt new transmission ofeach TB (or CW). Alternatively, if an ACK or NACK state is receivedthrough a single PHICH and retransmission is indicated through a PDCCHindicator, it is possible to attempt retransmission of each TB (or CW).In this case, if an indicator indicating new transmission orretransmission of two TBs (or two CWs) exists, new transmission orretransmission for each TB (or CW) can be independently performed. Thatis, new transmission or retransmission for one TB (or CW) can beperformed irrespective of new transmission or retransmission of adifferent TB (or CW).

TABLE 19 PHICH ACK/NACK Indicator for Indicator for state 1st CW 2nd CWBehavior ACK New New New data transmission transmission transmissionNACK New Retransmission 1st CW: New data transmission transmission 2ndCW: Retransmission NACK Retransmission New 1st CW: Retransmissiontransmission 2nd CW: New data transmission NACK RetransmissionRetransmission Retransmission

For example, an indicator shown in Table 19 may be an NDI contained in aUL grant PDCCH. As can be seen from Table 19, if an ACK state isreceived through a single PHICH and new transmission is indicatedthrough a PDCCH indicator, it is possible to attempt new transmission ofeach TB (or CW). Alternatively, if an ACK or NACK state is receivedthrough a single PHICH and retransmission is indicated through a PDCCHindicator, it is possible to attempt retransmission of each TB (or CW).In this case, if an indicator indicating new transmission orretransmission of two TBs (or two CWs) exists, new transmission orretransmission for each TB (or CW) can be independently performed. Thatis, new transmission or retransmission for one TB (or CW) can beperformed irrespective of new transmission or retransmission of adifferent TB (or CW).

Embodiment 5-C

In accordance with Embodiment 5-C, if a single PHICH for UL MCWtransmission is transmitted (for example, if two TBs (or two CWs) aresuccessfully decoded, ACK is transmitted, and if decoding of at leastone of two TBs (or two CWs) fails, NACK is transmitted), theretransmission operation for ACK/NACK states indicated by a PHICH can bedefined as shown in Table 16. In this case, the order of layers mappedto two TBs (or two CWs) may be exchanged or swapped. For example, theCW-to-layer mapping swap can be defined as shown in Table 20.

TABLE 20 First codeword Second codeword First transmission First layerSecond layer Second transmission Second layer First layer Thirdtransmission First layer Second layer Fourth transmission Second layerFirst layer

If the layers to which the codewords are mapped are swapped uponretransmission, a codeword decoding success rate can be increased. Forexample, if a first codeword is transmitted via a first layer and asecond codeword is transmitted via a second layer upon firsttransmission, the channel state of the first layer may be better thanthat of the second layer and thus the first codeword may be successfullydecoded, but decoding of the second codeword may fail. In this case, ifcodeword-to-layer mapping is not swapped upon retransmission, the secondcodeword is retransmitted via the second layer having a worse channelstate and thus decoding of the second codeword may fail. In contrast, ifcodeword-to-layer mapping is swapped upon retransmission, the secondcodeword is transmitted via the first layer having a better channelstate and a decoding success rate of the second codeword can beincreased.

6. DCI Configuration for HARQ Operation in UL MCW Transmission

In a conventional 3GPP LTE system, a single codeword is transmitted inuplink transmission and uplink scheduling information thereof may begiven via a PDCCH having DCI format 0. The existing DCI format 0 may bedefined as shown in Table 21.

TABLE 21 Contents Number of bits Flag for format 0/format 1Adifferentiation 1 bit Hopping flag 1 bit Resource block assignment andhopping resource N bits allocation Modulation and coding scheme andredundancy version 5 bits New data indicator 1 bit TPC command forscheduled PUSCH 2 bits Cyclic shift for DMRS 3 bits UL index (for TDD) 2bits Downlink Assignment Index (for TDD) 2 bits CQI request 1 bit

In DCI format 0, a “Flag for format 0/format 1A differentiation” fieldis a field for differentiating between DCI format 0 and DCI format 1A.Since DCI format 1A is a DCI format for scheduling downlink transmissionand has the same payload size as DCI format 0, a field fordifferentiating between DCI format 0 and DCI format 1A is included whileDCI format 0 and DCI format 1A have the same format. The “Flag forformat 0/format 1A differentiation” field having a value of 0 indicatesDCI format 0 and the “Flag for format 0/format 1A differentiation” fieldhaving a value of 1 indicates DCI format 1A.

A “Hopping flag” (frequency hopping flag) field indicates whether PUSCHfrequency hopping is applied. The “Hopping flag” field having a value of0 indicates that PUSCH frequency hopping is not applied and the “Hoppingflag” field having a value of 1 indicates that PUSCH frequency hoppingis applied.

A “Resource block assignment and hopping resource allocation” fieldindicates resource block assignment information of an uplink subframedepending on whether PUSCH frequency hopping is applied.

A “Modulation and coding scheme and redundancy version” field indicatesmodulation order and a redundancy version (RV) of a PUSCH. The RVindicates information about which subpacket is retransmitted in case ofretransmission. Among 32 states represented by 5 bits, 0 to 28 may beused to indicate modulation order and 29 to 31 may be used to indicateRV indexes 1, 2 and 3.

A “New data indicator” field indicates whether uplink schedulinginformation is for new data or retransmitted data. If the value of thisfield is toggled from an NDI value of previous transmission, thisindicates that new data is transmitted and, if the value of this fieldis not toggled from an NDI value of previous transmission, thisindicates that data is retransmitted.

A “TPC command for scheduled PUSCH” field indicates a value for decidingtransmit power of PUSCH transmission.

A “Cyclic shift for DMRS” field is a cyclic shift value used to generatea sequence for a demodulation reference signal (DMRS). The DMRS is areference signal used to estimate an uplink channel per antenna port orlayer.

A “UL index (for TDD)” field may indicate a subframe index set to uplinktransmission in a specific uplink-downlink configuration if a radioframe is configured using a time division duplexing (TDD) scheme.

A “Downlink Assignment Index (for TDD)” field may indicate a totalnumber of subframes set to PDSCH transmission in a specificuplink-downlink configuration if a radio frame is configured using a TDDscheme.

A “channel quality indicator (CQI) request” field indicates a requestfor reporting aperiodic channel quality information (CQI), a precodingmatrix indicator (PMI) and a rank indicator (RI) using a PUSCH. If the“CQI request” field is set to 1, a UE transmits a report for aperiodicCQI, PMI and RI using a PUSCH.

Meanwhile, a PDCCH of DCI format 2 for scheduling transmission ofmultiple downlink codewords may include control information shown inTable 22.

TABLE 22 Contents Number of bits Resource allocation header (resource 1bit allocation type 0/type 1) Resource block assignment and hopping Nbits resource allocation TPC command for PUCCH 2 bits DownlinkAssignment Index (for TDD) 2 bits HARQ process number 3 bits (FDD), 4bits (TDD) Transport block to codeword swap flag 1 bit For 1^(st)codeword Modulation and 5 bits coding scheme New data indicator 1 bitRedundancy version 2 bits For 2^(nd) codeword Modulation and 5 bitscoding scheme New data indicator 1 bit Redundancy version 2 bitsPrecoding information 3 bits (2 transmit antennas at eNode-B) 6 bits (4transmit antennas at eNode-B)

In DCI format 2, a “Resource allocation header (resource allocation type0/type 1)” field having a value of 0 indicates resource allocation ofType 0 and a “Resource allocation header (resource allocation type0/type 1)” field having a value of 1 indicates resource allocation ofType 1. Resource allocation of Type 0 may indicate that resource blockgroups (RBGs) allocated to a scheduled UE are a set of contiguousphysical resource blocks (PRBs). Resource allocation of Type 1 mayindicate physical resource blocks allocated to a scheduled UE in a setof physical resource blocks of one RBG selected from a subset of apredetermined number of RBGs.

A “Resource block assignment” field indicates a resource block allocatedto a scheduled UE according to resource assignment of Type 0 or Type 1.

A “TPC command for PUCCH” field indicates a value for deciding transmitpower of PUCCH transmission.

A “Downlink Assignment Index (for TDD)” field may indicate a totalnumber of subframes set to PDSCH transmission in a specificuplink-downlink configuration if a radio frame is configured using a TDDscheme.

A “HARQ process number” field may indicate which of a plurality of HARQprocesses managed by a HARQ entity is used for transmission.

A “Transport block to codeword swap flag” field indicates a transportblock-to-codeword mapping relationship if two transport blocks areenabled. If the “Transport block to codeword swap flag” field has avalue of 0, this indicates that a transport block 1 is mapped to acodeword 0 and a transport block 2 is mapped to a codeword 1, and, ifthe “Transport block to codeword swap flag” field has a value of 1, thisindicates that a transport block 2 is mapped to a codeword 0 and atransport block 1 is mapped to a codeword 1.

In DCI format 2, a “Modulation and coding scheme” field, a “New dataindicator” field and a “redundancy version” field are defined withrespect to a first codeword and a second codeword. The “Modulation andcoding scheme” field indicates a modulation order of a PUSCH. The “Newdata indicator” field indicates whether downlink scheduling informationis new data or retransmitted data. The “Redundancy version” fieldindicates information about which subpacket is retransmitted in case ofretransmission.

A “precoding information” field may indicate a codebook index forprecoding of downlink transmission. If a BS includes two transmitantennas, 3 bits are necessary to indicate codebook indexes of Rank 1and Rank 2 and six bits are necessary to indicate codebook indexes ofRanks 1, 2, 3 and 4.

As described above with reference to Tables 21 and 22, in the existing3GPP LTE system, DCI format 0 for transmission of a single uplinkcodeword and DCI format 2 for transmission of multiple downlinkcodewords are defined and a PDCCH DCI format for transmission ofmultiple uplink codewords is not defined.

In the present invention, examples of a new DCI format for transmissionof multiple uplink codewords (uplink grant via a PDCCH) are proposed asshown in Tables 23, 24 and 25.

TABLE 23 Contents Number of bits

Hopping flag 1 bit Resource block assignment and hopping N bits resourceallocation

TPC command for scheduled PUSCH 2 bits Cyclic shift for DMRS 3 bits ULindex (for TDD) 2 bits Downlink Assignment Index (for TDD) 2 bits CQIrequest 1 bit Resource allocation header (resource 1 bit allocation type0/type 1)

TPC command for PUCCH 2 bits Downlink Assignment Index (for TDD) 2 bits

Transport block to codeword swap flag 1 bit For 1^(st) codewordModulation and 5 bits coding scheme and redundancy version New dataindicator 1 bit

For 2^(nd) codeword Modulation and 5 bits coding scheme and redundancyversion New data indicator 1 bit

Precoding information 3 bits/N-bits (2 transmit antennas at eNode-B) 6bits/N-bits (4 transmit antennas at eNode-B)

Table 23 shows an example of a new DCI format used to schedule a PUSCHin a multiple antenna port transmission mode in one uplink cell (or onecomponent carrier). A DCI format defined in Table 23 may be referred toas a format index (e.g., DCI format 4) for differentiation from thepreviously defined DCI format.

In Table 23, fields that have been struck through indicate some fieldswhich are not present in a PDCCH DCI format for UL MCW transmissionwhereas they are present in DCI format 0 (See Table 21) and DCI format 2(See Table 22). Underlined fields indicate fields added to DCI format 0(See Table 21) and DCI format 2 (Table 22).

A “Hopping flag” (frequency hopping flag) field may indicate whetherPUSCH frequency hopping is applied. The “Hopping flag” field may bedefined if contiguous resource assignment is applied to a PUSCH and maybe omitted if non-contiguous resource assignment is applied to a PUSCH.

A “Resource block assignment and hopping resource allocation” field mayindicate resource block assignment information of an uplink subframedepending on whether PUSCH frequency hopping is applied or singlecluster assignment or multiple cluster assignment is applied.

A “TPC command for scheduled PUSCH” field indicates a value for decidingtransmit power of PUSCH transmission. The “TPC command for scheduledPUSCH” field may be defined by 2 bits if an uplink transmitter (e.g., aUE)-specific transmit power control (TPC) command is given.Alternatively, if a TPC command is given with respect to each of aplurality of antennas, the “TPC command for scheduled PUSCH” field maybe defined by a bit size of 2 bits×the number of antennas. A TPC commandmay be given with respect to each of two codewords and, in this case,the “TPC command for scheduled PUSCH” field may be defined by a size of4 bits.

A “Cyclic shift for DMRS” field is a cyclic shift value used to generatea sequence for a demodulation reference signal (DMRS). The “Cyclic shiftfor DMRS” field may include an orthogonal cover code (OCC) index used toadditionally generate a DMRS. A cyclic shift value of one layer (or oneantenna port) may be given by the “Cyclic shift for DMRS” field. Acyclic shift value of another layer (or another antenna port) may becomputed from the cyclic shift value given according to a predeterminedrule based on the above layer (or antenna port).

A “UL index (for TDD)” field may indicate a subframe index set to uplinktransmission in a specific uplink-downlink configuration if a radioframe is configured using a time division duplexing (TDD) scheme.

A “Downlink Assignment Index (for TDD)” field may indicate a totalnumber of subframes set to PDSCH transmission in a specificuplink-downlink configuration if a radio frame is configured using a TDDscheme.

A “channel quality information (CQI) request” field indicates a requestfor reporting aperiodic CQI, a precoding matrix indicator (PMI) and arank indicator (RI) using a PUSCH.

A “Resource allocation header (resource allocation type 0/type 1)” fieldmay indicate resource allocation of Type 0 or Type 1. Type 0 mayindicate contiguous resource allocation and Type 1 may indicate avariety of other forms of resource allocation. For example, Type 1 mayindicate non-contiguous resource allocation. If a PUSCH resourceallocation scheme is indicated via explicit or implicit signaling, the“Resource allocation header (resource allocation type 0/type 1)” fieldmay be omitted.

A “TPC command for PUCCH” field may indicate a value for decidingtransmit power of PUCCH transmission and may be omitted in some cases.

A “Transport block to codeword swap flag” field indicates a transportblock-to-codeword mapping relationship if two transport blocks areenabled. If the “Transport block to codeword swap flag” field has avalue of 0, this indicates that a transport block 1 is mapped to acodeword 0 and a transport block 2 is mapped to a codeword 1, and, ifthe “Transport block to codeword swap flag” field has a value of 1, thisindicates that a transport block 2 is mapped to a codeword 0 and atransport block 1 is mapped to a codeword 1. If one of the two codewordsis disabled, the “Transport block to codeword swap flag” field isreserved. Alternatively, if transport block to codeword swapping is notsupported, the “Transport block to codeword swap flag” field may beomitted.

A “Modulation and coding scheme” and a “new data indicator” field may bedefined with respect to two codewords (or transport blocks).

A “Modulation and coding scheme” field indicates a modulation order ofeach codeword (or each transport block). Some bit states of the“Modulation and coding scheme” field may be used to indicate RVinformation of each codeword (or each transport block). The RV mayindicate information about which subpacket is retransmitted in case ofretransmission of each codeword (or each transport block).

A “New data indicator” field indicates whether uplink schedulinginformation of each codeword (or each transport block) is new data orretransmitted data. If the value of this field is toggled from an NDIvalue of previous transmission of the codeword (or the transport block),this indicates that new data is transmitted and, if the value of thisfield is not toggled from an NDI value of previous transmission of thecodeword (or the transport block), this indicates that data isretransmitted.

A “precoding information” field may indicate a codebook index forprecoding of downlink transmission. If an uplink transmitter (e.g., aUE) includes two transmit antennas, the “precoding information” fieldmay be defined by 3 bits in order to indicate codebook indexes of Rank 1and Rank 2 and, if an uplink transmitter (e.g., a UE) includes fourtransmit antennas, the “precoding information” field may be defined by 6bits in order to indicate codebook indexes of Rank 1, 2, 3 and 4.

Table 24 shows another example of a new DCI format used to schedule aPUSCH in a multiple antenna port transmission mode in one uplink cell(or one component carrier). A DCI format defined in Table 24 may bereferred to as a format index (e.g., DCI format 4) for differentiationfrom the previously defined DCI format.

TABLE 24 Contents Number of bits Resource allocation header (resource 1bit allocation type 0/type 1) Hopping flag 1 bit Resource blockassignment and hopping N bits resource allocation TPC command forscheduled PUSCH 2 bits Cyclic shift for DMRS 3 bits + N(0~3) bits BTPCcommand for PUCCH 2 bits Transport block to codeword swap flag 1 bit For1^(st) codeword Modulation and 5 bits coding scheme and redundancyversion New data indicator 1 bit For 2^(nd) Modulation and 5 bitscodeword coding scheme and redundancy version New data indicator 1 bitPrecoding information 3 bits/N-bits (2 transmit antennas at eNode-B) 6bits/N-bits (4 transmit antennas at eNode-B) CQI request 1 bit UL index(for TDD) 2 bits Downlink Assignment Index (for TDD) 2 bits DownlinkAssignment Index (for TDD) 2 bits

Among the fields defined in the DCI format of Table 24, a description ofthe same fields as those of the DCI format of Table 23 will be omittedfor clarity of description.

In the DCI format of Table 24, a “Cyclic shift for DMRS” field mayindicate a cyclic shift value used to generate a sequence for an uplinkDMRS. The “Cyclic shift for DMRS” field may include an OCC index used toadditionally generate a DMRS. Through the “Cyclic shift for DMRS” field,cyclic shift values of a plurality of layers (or antenna ports) may beexplicitly given. For example, one cyclic shift value may be representedby 3 bits and the “Cyclic shift for DMRS” field may be defined by a sizeof 12 bits in order to indicate the respective cyclic shift values offour layers (or four antenna ports).

The remaining fields of the DCI format of Table 24 are equal to those ofthe DCI format of Table 23.

Table 25 shows another example of a new DCI format used to schedule aPUSCH in a multiple antenna port transmission mode in one uplink cell(or one component carrier). A DCI format defined in Table 25 may bereferred to as a format index (e.g., DCI format 4) for differentiationfrom the previously defined DCI format.

TABLE 25 Contents Number of bits Resource allocation header (resource 1bit allocation type 0/type 1) Hopping flag 1 bit Resource blockassignment and hopping N bits resource allocation TPC command forscheduled PUSCH 2 bits Cyclic shift for DMRS 3 bits + N(0~3) bits TPCcommand for PUCCH 2 bits New data indicator 1 bit Transport block tocodeword swap flag 1 bit Modulation and coding scheme and 5 bitsredundancy version for 1^(st) codeword Modulation and coding scheme and5 bits redundancy version for 2^(nd) codeword Precoding information 3bits/N-bits (2 transmit antennas at eNode-B) 6 bits/N-bits (4 transmitantennas at eNode-B) CQI request 1 bit UL index (for TDD) 2 bitsDownlink Assignment Index (for TDD) 2 bits Downlink Assignment Index(for TDD) 2 bits

Among the fields defined in the DCI format of Table 25, a description ofthe same fields as those of the DCI format of Table 23 will be omittedfor clarity of description.

In the DCI format of Table 25, a “Cyclic shift for DMRS” field mayindicate a cyclic shift value used to generate a sequence for an uplinkDMRS. The “Cyclic shift for DMRS” field may include an OCC index used toadditionally generate a DMRS. By the “Cyclic shift for DMRS” field,cyclic shift values of 2 layers (or 2 antenna ports) may be explicitlygiven. For example, one cyclic shift value may be represented by 3 bitsand the “Cyclic shift for DMRS” field may be defined by a size of 12bits in order to indicate the respective cyclic shift values of fourlayers (or four antenna ports).

While the “New data indicator” fields of the codewords are defined inthe DCI format of Table 23 or 24, only one “New data indicator” fieldmay be defined with respect to two codewords in the DCI format of Table25. That is, two codewords (or two transport blocks) are bundled toindicate whether uplink scheduling information is for new data orretransmitted data. If the value of this field is toggled from an NDIvalue of previous transmission, the two codewords (or two transportblocks) indicate new data transmission and, if the value of this fieldis not toggled from an NDI value of previous transmission, the twocodewords (or two transport blocks) indicate retransmission.

The remaining fields of the DCI format of Table 25 are equal to those ofthe DCI format of Table 9.

In the DCI formats of Tables 23, 24 and 25, a “Carrier Indicator” fieldand a “Multi-cluster flag” field may be additionally defined. The“Carrier Indicator” field may indicate which uplink cell (or componentcarrier) is used to schedule MCW PUSCH transmission if one or moreuplink cells (or one or more component carriers) are present, and may berepresented by 0 or 3 bits. The “Multi-cluster flag” field may indicatewhether multi-cluster allocation is applied in terms of uplink resourceallocation.

FIG. 10 is a flowchart illustrating uplink MIMO transmission andreception methods according to embodiments of the present invention.

Referring to FIG. 10, a BS can transmit a UL grant PDCCH to a UE in stepS1010. The UL grant PDCCH may include control information based on a DCIformat scheduling transmission of multiple data blocks (i.e., multipleTBs).

The UE can transmit multiple TBs scheduled according to the UL grantPDCCH to the BS.

In step S1030, the BS may attempt to decode each of the received TBs,such that it can transmit ACK/NACK information of each TB to the UEthrough a PHICH.

The UE can retransmit a TB indicating NACK to the BS in step S1040. Instep S1040, if the number of NACK TBs is not identical to the number ofTBs indicated by a PDCCH of step S1010, a precoding matrix for the samenumber of transmission (Tx) layers as the number of layers correspondingto a NACK TB can be utilized in retransmission. That is, whenretransmission of NACK TB is performed at step S1040 on the conditionthat the number of TBs indicated by a PDCCH is 2 and the number of NACKTBs is 1, one case in which the number of layers mapped to a codeword(i.e., one CW) mapped to NACK TBs is 1 may occur or another case inwhich the number of layers mapped to a codeword mapped to NACK TBs is 2may occur. In this case, if the number of layers mapped to NACK TBs (orNACK CWs) is 1, a specific precoder from among precoders defined for onetransmission (Tx) layer (i.e., Rank=1) can be used in retransmission.Alternatively, if the number of layers mapped to NACK TBs (or NACK CWs)is 2, a specific precoder from among precoders defined for two Tx layers(i.e., Rank=2) can be used in retransmission.

Here, retransmission of step S1040 may be performed when a PDCCH is notdetected in a DL subframe (i.e., subframe of step S1030) through whichthe UE detects a PHICH. That is, if the HARQ operation is performed byACK/NACK information indicated by a PHICH without using the UL grantPDCCH, the above-mentioned retransmission can be carried out.

In association with a precoding matrix used for retransmission, aprecoder suitable for the number of Tx layers used in the aboveretransmission, from among precoding matrices indicated by the mostrecent PDCCH, can be used. In more detail, a precoding matrix, that issuitable for the number of layers mapped to retransmitted TBs (or CWs)from among the precoding matrices indicated by the most recent PDCCH,can be used for retransmission.

In addition, ACK/NACK information of each TB can be indicated throughmultiple PHICH resources. That is, one PHICH resource may be allocatedto one TB.

In association with the UL MIMO transmission and reception method asshown in FIG. 10, the contents described in the above-mentionedembodiments may be used independently of each other or two or moreembodiments may be simultaneously applied, and the same parts may beomitted herein for convenience and clarity of description.

In addition, the principles of the present invention may also be appliedto the UL MIMO transmission and reception according to the presentinvention in association with not only MIMO transmission between a basestation (BS) and a relay node (RN) (for use in a backhaul uplink and abackhaul downlink) but also MIMO transmission between an RN and a UE(for use in an access uplink and an access downlink).

FIG. 11 is a block diagram of an eNB apparatus and a UE apparatusaccording to an embodiment of the present invention.

Referring to FIG. 11, an eNB apparatus 1110 may include a reception (Rx)module 1111, a transmission (Tx) module 1112, a processor 1113, a memory1114, and a plurality of antennas 1115. The plurality of antennas 1115may be contained in the eNB apparatus supporting MIMO transmission andreception. The reception (Rx) module 1111 may receive a variety ofsignals, data and information on uplink starting from the UE. Thetransmission (Tx) module 1112 may transmit a variety of signals, dataand information on downlink for the UE. The processor 1113 may provideoverall control to the eNB apparatus 1110.

The eNB apparatus 1110 according to one embodiment of the presentinvention may be constructed to transmit control information of UL MIMOtransmission. The processor 1113 of the eNB apparatus 1110 may enablethe Tx module 1112 to transmit a DCI scheduling UL transmission of aplurality of TBs to a UE over a PDCCH. In addition, the processor 1113may enable the Rx module 1111 to receive a plurality of TBs scheduled byDCI from a UE. In addition, the processor 1113 may enable the Tx module1112 to transmit ACK or NACK indication information of each reception TBto the UE over a PHICH. In addition, the processor 1113 may enable theRx module 1111 to receive retransmission information of a NACK TB fromthe UE. In this case, if the number of NACK TBs is not identical to thenumber of TBs indicated by a PDCCH, a precoding matrix for the samenumber of Tx layers as the number of layers corresponding to NACK TB canbe used in retransmission.

The processor 1113 of the eNB apparatus 1110 processes informationreceived at the eNB apparatus 1110 and transmission information. Thememory 1114 may store the processed information for a predeterminedtime. The memory 1114 may be replaced with a component such as a buffer(not shown).

Referring to FIG. 11, a UE apparatus 1120 may include a reception (Rx)module 1121, a transmission (Tx) module 1122, a processor 1123, a memory1124, and a plurality of antennas 1125. The plurality of antennas 1125may be contained in the UE apparatus supporting MIMO transmission andreception. The reception (Rx) module 1121 may receive a variety ofsignals, data and information on downlink starting from the eNB. Thetransmission (Tx) module 1122 may transmit a variety of signals, dataand information on uplink for the eNB. The processor 1123 may provideoverall control to the UE apparatus 1120.

The UE apparatus 1120 according to one embodiment of the presentinvention may be constructed to perform UL MIMO transmission. Theprocessor 1123 of the UE apparatus 1120 may enable the Rx module 1121 toreceive a DCI scheduling UL transmission of a plurality of TBs from a UEover a PDCCH. In addition, the processor 1123 may enable the Tx module1122 to transmit a plurality of TBs scheduled by DCI to the eNB. Inaddition, the processor 1123 may enable the Rx module 1121 to receiveACK or NACK indication information of each reception TB from the eNBover a PHICH. In addition, the processor 1123 may enable the Tx module1122 to transmit retransmission information of a NACK TB to the eNB. Inthis case, if the number of NACK TBs is not identical to the number ofTBs indicated by a PDCCH, a precoding matrix for the same number of Txlayers as the number of layers corresponding to NACK TB can be used inretransmission.

The processor 1123 of the UE apparatus 1120 processes informationreceived at the UE apparatus 1120 and transmission information. Thememory 1124 may store the processed information for a predeterminedtime. The memory 1124 may be replaced with a component such as a buffer(not shown).

The specific configurations of the above eNB and UE apparatuses may beimplemented such that the various embodiments of the present inventionare performed independently or two or more embodiments of the presentinvention are performed simultaneously. Redundant matters will not bedescribed herein for clarity.

The eNB apparatus 1110 shown in FIG. 11 may also be applied to a relaynode (RN) acting as a DL transmission entity or UL reception entity, andthe UE apparatus 1120 shown in FIG. 11 may also be applied to a relaynode (RN) acting as a DL reception entity or UL transmission entity.

The above-described embodiments of the present invention can beimplemented by a variety of means, for example, hardware, firmware,software, or a combination of them.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs),field programmable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. For example, those skilledin the art may use each construction described in the above embodimentsin combination with each other. Accordingly, the invention should not belimited to the specific embodiments described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above exemplary embodiments are therefore to beconstrued in all aspects as illustrative and not restrictive. The scopeof the invention should be determined by the appended claims and theirlegal equivalents, not by the above description, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. Also, it will be obvious to thoseskilled in the art that claims that are not explicitly cited in theappended claims may be presented in combination as an exemplaryembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to a variety ofmobile communication systems.

The invention claimed is:
 1. A method by a base station (BS) for receiving an uplink (UL) Multiple Input Multiple Output (MIMO) retransmission, the method comprising: receiving a retransmission of at least one negatively-acknowledged transport block (TB) from a user equipment (UE), wherein, if downlink control information for the retransmission has not been previously transmitted by the BS to the UE and if a number of the at least one negatively-acknowledged TB is different from a number of TBs as indicated by a most recently transmitted downlink control information, a predetermined precoding matrix is used in the retransmission, and wherein a number of transmission layers for the predetermined precoding matrix is equal to a number of transmission layers corresponding to the negatively-acknowledged TB.
 2. The method according to claim 1, wherein the negatively-acknowledged TB is indicated by a physical hybrid-automatic repeat request indicator channel (PHICH).
 3. The method according to claim 2, wherein a subframe in which the retransmission by the UE is performed corresponds to subframe index n+4 if a subframe in which the UE receives the PHICH corresponds to subframe index n, where n is an integer and n≧0.
 4. A method by a user equipment (UE) for performing uplink (UL) Multiple Input Multiple Output (MIMO) retransmission, the method comprising: performing, by the UE, a retransmission of at least one negatively-acknowledged transport block (TB) to a Base Station (BS), wherein, if downlink control information from the BS for the retransmission is not detected by the UE and if a number of the at least one negatively-acknowledged TB is different from a number of TBs as indicated by a most recently received downlink control information, a predetermined precoding matrix is used in the retransmission, and wherein a number of transmission layers for the predetermined precoding matrix is equal to a number of transmission layers corresponding to the negatively-acknowledged TB.
 5. The method according to claim 4, wherein the negatively-acknowledged TB is indicated by a physical hybrid-automatic repeat request indicator channel (PHICH).
 6. The method according to claim 5, wherein a subframe in which the retransmission is performed corresponds to subframe index n+4 if a subframe in which the UE receives the PHICH corresponds to subframe index n, where n is an integer and n≧0.
 7. A base station (BS) for transmitting control information for uplink (UL) Multiple Input Multiple Output (MIMO) transmission, the BS comprising: a reception module; a transmission module; and a processor, wherein the processor is configured to: receive, from a user equipment (UE), a retransmission of at least one negatively-acknowledged transport block (TB), wherein, if downlink control information for the retransmission has not been previously transmitted by the BS to the UE and if a number of the at least one negatively-acknowledged TB is different from a number of TBs as indicated by a most recently transmitted downlink control information, a predetermined precoding matrix is used in the retransmission, and wherein a number of transmission layers for the predetermined precoding matrix is equal to a number of transmission layers corresponding to the negatively-acknowledged TB.
 8. The BS according to claim 7, wherein the negatively-acknowledged TB is indicated by a physical hybrid-automatic repeat request indicator channel (PHICH).
 9. The BS according to claim 8, wherein a subframe in which the retransmission by the UE is performed corresponds to subframe index n+4 if a subframe in which the UE receives the PHICH corresponds to subframe index n, where n is an integer and n≧0.
 10. A user equipment (UE) for performing uplink (UL) Multiple Input Multiple Output (MIMO) transmission, the UE comprising: a reception module; a transmission module; and a processor, wherein the processor is configured to: perform a retransmission of at least one negatively-acknowledged transport block (TB) to a Base Station (BS), wherein, if downlink control information from the BS for the retransmission is not detected by the UE and if a number of the at least one negatively-acknowledged TB is different from a number of TBs as indicated by the most recently received downlink control information, a predetermined precoding matrix is used in the retransmission, and wherein a number of transmission layers for the predetermined precoding matrix is equal to a number of transmission layers corresponding to the negatively-acknowledged TB.
 11. The UE according to claim 10, wherein the negatively-acknowledged TB is indicated by a physical hybrid-automatic repeat request indicator channel (PHICH).
 12. The UE according to claim 11, wherein a subframe in which the retransmission is performed corresponds to subframe index n+4 if a subframe in which the UE receives the PHICH corresponds to subframe index n, where n is an integer and n≧0. 